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1 | '\" te | |
2 | .\" Copyright (c) 2013 by Turbo Fredriksson <turbo@bayour.com>. All rights reserved. | |
3 | .\" Copyright (c) 2017 Datto Inc. | |
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5 | .\" and Distribution License (the "License"). You may not use this file except | |
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7 | .\" usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing. | |
8 | .\" | |
9 | .\" See the License for the specific language governing permissions and | |
10 | .\" limitations under the License. When distributing Covered Code, include this | |
11 | .\" CDDL HEADER in each file and include the License file at | |
12 | .\" usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this | |
13 | .\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your | |
14 | .\" own identifying information: | |
15 | .\" Portions Copyright [yyyy] [name of copyright owner] | |
16 | .TH ZFS-MODULE-PARAMETERS 5 "Oct 28, 2017" | |
17 | .SH NAME | |
18 | zfs\-module\-parameters \- ZFS module parameters | |
19 | .SH DESCRIPTION | |
20 | .sp | |
21 | .LP | |
22 | Description of the different parameters to the ZFS module. | |
23 | ||
24 | .SS "Module parameters" | |
25 | .sp | |
26 | .LP | |
27 | ||
28 | .sp | |
29 | .ne 2 | |
30 | .na | |
31 | \fBdbuf_cache_max_bytes\fR (ulong) | |
32 | .ad | |
33 | .RS 12n | |
34 | Maximum size in bytes of the dbuf cache. When \fB0\fR this value will default | |
35 | to \fB1/2^dbuf_cache_shift\fR (1/32) of the target ARC size, otherwise the | |
36 | provided value in bytes will be used. The behavior of the dbuf cache and its | |
37 | associated settings can be observed via the \fB/proc/spl/kstat/zfs/dbufstats\fR | |
38 | kstat. | |
39 | .sp | |
40 | Default value: \fB0\fR. | |
41 | .RE | |
42 | ||
43 | .sp | |
44 | .ne 2 | |
45 | .na | |
46 | \fBdbuf_cache_hiwater_pct\fR (uint) | |
47 | .ad | |
48 | .RS 12n | |
49 | The percentage over \fBdbuf_cache_max_bytes\fR when dbufs must be evicted | |
50 | directly. | |
51 | .sp | |
52 | Default value: \fB10\fR%. | |
53 | .RE | |
54 | ||
55 | .sp | |
56 | .ne 2 | |
57 | .na | |
58 | \fBdbuf_cache_lowater_pct\fR (uint) | |
59 | .ad | |
60 | .RS 12n | |
61 | The percentage below \fBdbuf_cache_max_bytes\fR when the evict thread stops | |
62 | evicting dbufs. | |
63 | .sp | |
64 | Default value: \fB10\fR%. | |
65 | .RE | |
66 | ||
67 | .sp | |
68 | .ne 2 | |
69 | .na | |
70 | \fBdbuf_cache_shift\fR (int) | |
71 | .ad | |
72 | .RS 12n | |
73 | Set the size of the dbuf cache, \fBdbuf_cache_max_bytes\fR, to a log2 fraction | |
74 | of the target arc size. | |
75 | .sp | |
76 | Default value: \fB5\fR. | |
77 | .RE | |
78 | ||
79 | .sp | |
80 | .ne 2 | |
81 | .na | |
82 | \fBignore_hole_birth\fR (int) | |
83 | .ad | |
84 | .RS 12n | |
85 | When set, the hole_birth optimization will not be used, and all holes will | |
86 | always be sent on zfs send. Useful if you suspect your datasets are affected | |
87 | by a bug in hole_birth. | |
88 | .sp | |
89 | Use \fB1\fR for on (default) and \fB0\fR for off. | |
90 | .RE | |
91 | ||
92 | .sp | |
93 | .ne 2 | |
94 | .na | |
95 | \fBl2arc_feed_again\fR (int) | |
96 | .ad | |
97 | .RS 12n | |
98 | Turbo L2ARC warm-up. When the L2ARC is cold the fill interval will be set as | |
99 | fast as possible. | |
100 | .sp | |
101 | Use \fB1\fR for yes (default) and \fB0\fR to disable. | |
102 | .RE | |
103 | ||
104 | .sp | |
105 | .ne 2 | |
106 | .na | |
107 | \fBl2arc_feed_min_ms\fR (ulong) | |
108 | .ad | |
109 | .RS 12n | |
110 | Min feed interval in milliseconds. Requires \fBl2arc_feed_again=1\fR and only | |
111 | applicable in related situations. | |
112 | .sp | |
113 | Default value: \fB200\fR. | |
114 | .RE | |
115 | ||
116 | .sp | |
117 | .ne 2 | |
118 | .na | |
119 | \fBl2arc_feed_secs\fR (ulong) | |
120 | .ad | |
121 | .RS 12n | |
122 | Seconds between L2ARC writing | |
123 | .sp | |
124 | Default value: \fB1\fR. | |
125 | .RE | |
126 | ||
127 | .sp | |
128 | .ne 2 | |
129 | .na | |
130 | \fBl2arc_headroom\fR (ulong) | |
131 | .ad | |
132 | .RS 12n | |
133 | How far through the ARC lists to search for L2ARC cacheable content, expressed | |
134 | as a multiplier of \fBl2arc_write_max\fR | |
135 | .sp | |
136 | Default value: \fB2\fR. | |
137 | .RE | |
138 | ||
139 | .sp | |
140 | .ne 2 | |
141 | .na | |
142 | \fBl2arc_headroom_boost\fR (ulong) | |
143 | .ad | |
144 | .RS 12n | |
145 | Scales \fBl2arc_headroom\fR by this percentage when L2ARC contents are being | |
146 | successfully compressed before writing. A value of 100 disables this feature. | |
147 | .sp | |
148 | Default value: \fB200\fR%. | |
149 | .RE | |
150 | ||
151 | .sp | |
152 | .ne 2 | |
153 | .na | |
154 | \fBl2arc_noprefetch\fR (int) | |
155 | .ad | |
156 | .RS 12n | |
157 | Do not write buffers to L2ARC if they were prefetched but not used by | |
158 | applications | |
159 | .sp | |
160 | Use \fB1\fR for yes (default) and \fB0\fR to disable. | |
161 | .RE | |
162 | ||
163 | .sp | |
164 | .ne 2 | |
165 | .na | |
166 | \fBl2arc_norw\fR (int) | |
167 | .ad | |
168 | .RS 12n | |
169 | No reads during writes | |
170 | .sp | |
171 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
172 | .RE | |
173 | ||
174 | .sp | |
175 | .ne 2 | |
176 | .na | |
177 | \fBl2arc_write_boost\fR (ulong) | |
178 | .ad | |
179 | .RS 12n | |
180 | Cold L2ARC devices will have \fBl2arc_write_max\fR increased by this amount | |
181 | while they remain cold. | |
182 | .sp | |
183 | Default value: \fB8,388,608\fR. | |
184 | .RE | |
185 | ||
186 | .sp | |
187 | .ne 2 | |
188 | .na | |
189 | \fBl2arc_write_max\fR (ulong) | |
190 | .ad | |
191 | .RS 12n | |
192 | Max write bytes per interval | |
193 | .sp | |
194 | Default value: \fB8,388,608\fR. | |
195 | .RE | |
196 | ||
197 | .sp | |
198 | .ne 2 | |
199 | .na | |
200 | \fBmetaslab_aliquot\fR (ulong) | |
201 | .ad | |
202 | .RS 12n | |
203 | Metaslab granularity, in bytes. This is roughly similar to what would be | |
204 | referred to as the "stripe size" in traditional RAID arrays. In normal | |
205 | operation, ZFS will try to write this amount of data to a top-level vdev | |
206 | before moving on to the next one. | |
207 | .sp | |
208 | Default value: \fB524,288\fR. | |
209 | .RE | |
210 | ||
211 | .sp | |
212 | .ne 2 | |
213 | .na | |
214 | \fBmetaslab_bias_enabled\fR (int) | |
215 | .ad | |
216 | .RS 12n | |
217 | Enable metaslab group biasing based on its vdev's over- or under-utilization | |
218 | relative to the pool. | |
219 | .sp | |
220 | Use \fB1\fR for yes (default) and \fB0\fR for no. | |
221 | .RE | |
222 | ||
223 | .sp | |
224 | .ne 2 | |
225 | .na | |
226 | \fBzfs_metaslab_segment_weight_enabled\fR (int) | |
227 | .ad | |
228 | .RS 12n | |
229 | Enable/disable segment-based metaslab selection. | |
230 | .sp | |
231 | Use \fB1\fR for yes (default) and \fB0\fR for no. | |
232 | .RE | |
233 | ||
234 | .sp | |
235 | .ne 2 | |
236 | .na | |
237 | \fBzfs_metaslab_switch_threshold\fR (int) | |
238 | .ad | |
239 | .RS 12n | |
240 | When using segment-based metaslab selection, continue allocating | |
241 | from the active metaslab until \fBzfs_metaslab_switch_threshold\fR | |
242 | worth of buckets have been exhausted. | |
243 | .sp | |
244 | Default value: \fB2\fR. | |
245 | .RE | |
246 | ||
247 | .sp | |
248 | .ne 2 | |
249 | .na | |
250 | \fBmetaslab_debug_load\fR (int) | |
251 | .ad | |
252 | .RS 12n | |
253 | Load all metaslabs during pool import. | |
254 | .sp | |
255 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
256 | .RE | |
257 | ||
258 | .sp | |
259 | .ne 2 | |
260 | .na | |
261 | \fBmetaslab_debug_unload\fR (int) | |
262 | .ad | |
263 | .RS 12n | |
264 | Prevent metaslabs from being unloaded. | |
265 | .sp | |
266 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
267 | .RE | |
268 | ||
269 | .sp | |
270 | .ne 2 | |
271 | .na | |
272 | \fBmetaslab_fragmentation_factor_enabled\fR (int) | |
273 | .ad | |
274 | .RS 12n | |
275 | Enable use of the fragmentation metric in computing metaslab weights. | |
276 | .sp | |
277 | Use \fB1\fR for yes (default) and \fB0\fR for no. | |
278 | .RE | |
279 | ||
280 | .sp | |
281 | .ne 2 | |
282 | .na | |
283 | \fBmetaslabs_per_vdev\fR (int) | |
284 | .ad | |
285 | .RS 12n | |
286 | When a vdev is added, it will be divided into approximately (but no more than) this number of metaslabs. | |
287 | .sp | |
288 | Default value: \fB200\fR. | |
289 | .RE | |
290 | ||
291 | .sp | |
292 | .ne 2 | |
293 | .na | |
294 | \fBmetaslab_preload_enabled\fR (int) | |
295 | .ad | |
296 | .RS 12n | |
297 | Enable metaslab group preloading. | |
298 | .sp | |
299 | Use \fB1\fR for yes (default) and \fB0\fR for no. | |
300 | .RE | |
301 | ||
302 | .sp | |
303 | .ne 2 | |
304 | .na | |
305 | \fBmetaslab_lba_weighting_enabled\fR (int) | |
306 | .ad | |
307 | .RS 12n | |
308 | Give more weight to metaslabs with lower LBAs, assuming they have | |
309 | greater bandwidth as is typically the case on a modern constant | |
310 | angular velocity disk drive. | |
311 | .sp | |
312 | Use \fB1\fR for yes (default) and \fB0\fR for no. | |
313 | .RE | |
314 | ||
315 | .sp | |
316 | .ne 2 | |
317 | .na | |
318 | \fBspa_config_path\fR (charp) | |
319 | .ad | |
320 | .RS 12n | |
321 | SPA config file | |
322 | .sp | |
323 | Default value: \fB/etc/zfs/zpool.cache\fR. | |
324 | .RE | |
325 | ||
326 | .sp | |
327 | .ne 2 | |
328 | .na | |
329 | \fBspa_asize_inflation\fR (int) | |
330 | .ad | |
331 | .RS 12n | |
332 | Multiplication factor used to estimate actual disk consumption from the | |
333 | size of data being written. The default value is a worst case estimate, | |
334 | but lower values may be valid for a given pool depending on its | |
335 | configuration. Pool administrators who understand the factors involved | |
336 | may wish to specify a more realistic inflation factor, particularly if | |
337 | they operate close to quota or capacity limits. | |
338 | .sp | |
339 | Default value: \fB24\fR. | |
340 | .RE | |
341 | ||
342 | .sp | |
343 | .ne 2 | |
344 | .na | |
345 | \fBspa_load_verify_data\fR (int) | |
346 | .ad | |
347 | .RS 12n | |
348 | Whether to traverse data blocks during an "extreme rewind" (\fB-X\fR) | |
349 | import. Use 0 to disable and 1 to enable. | |
350 | ||
351 | An extreme rewind import normally performs a full traversal of all | |
352 | blocks in the pool for verification. If this parameter is set to 0, | |
353 | the traversal skips non-metadata blocks. It can be toggled once the | |
354 | import has started to stop or start the traversal of non-metadata blocks. | |
355 | .sp | |
356 | Default value: \fB1\fR. | |
357 | .RE | |
358 | ||
359 | .sp | |
360 | .ne 2 | |
361 | .na | |
362 | \fBspa_load_verify_metadata\fR (int) | |
363 | .ad | |
364 | .RS 12n | |
365 | Whether to traverse blocks during an "extreme rewind" (\fB-X\fR) | |
366 | pool import. Use 0 to disable and 1 to enable. | |
367 | ||
368 | An extreme rewind import normally performs a full traversal of all | |
369 | blocks in the pool for verification. If this parameter is set to 0, | |
370 | the traversal is not performed. It can be toggled once the import has | |
371 | started to stop or start the traversal. | |
372 | .sp | |
373 | Default value: \fB1\fR. | |
374 | .RE | |
375 | ||
376 | .sp | |
377 | .ne 2 | |
378 | .na | |
379 | \fBspa_load_verify_maxinflight\fR (int) | |
380 | .ad | |
381 | .RS 12n | |
382 | Maximum concurrent I/Os during the traversal performed during an "extreme | |
383 | rewind" (\fB-X\fR) pool import. | |
384 | .sp | |
385 | Default value: \fB10000\fR. | |
386 | .RE | |
387 | ||
388 | .sp | |
389 | .ne 2 | |
390 | .na | |
391 | \fBspa_slop_shift\fR (int) | |
392 | .ad | |
393 | .RS 12n | |
394 | Normally, we don't allow the last 3.2% (1/(2^spa_slop_shift)) of space | |
395 | in the pool to be consumed. This ensures that we don't run the pool | |
396 | completely out of space, due to unaccounted changes (e.g. to the MOS). | |
397 | It also limits the worst-case time to allocate space. If we have | |
398 | less than this amount of free space, most ZPL operations (e.g. write, | |
399 | create) will return ENOSPC. | |
400 | .sp | |
401 | Default value: \fB5\fR. | |
402 | .RE | |
403 | ||
404 | .sp | |
405 | .ne 2 | |
406 | .na | |
407 | \fBzfetch_array_rd_sz\fR (ulong) | |
408 | .ad | |
409 | .RS 12n | |
410 | If prefetching is enabled, disable prefetching for reads larger than this size. | |
411 | .sp | |
412 | Default value: \fB1,048,576\fR. | |
413 | .RE | |
414 | ||
415 | .sp | |
416 | .ne 2 | |
417 | .na | |
418 | \fBzfetch_max_distance\fR (uint) | |
419 | .ad | |
420 | .RS 12n | |
421 | Max bytes to prefetch per stream (default 8MB). | |
422 | .sp | |
423 | Default value: \fB8,388,608\fR. | |
424 | .RE | |
425 | ||
426 | .sp | |
427 | .ne 2 | |
428 | .na | |
429 | \fBzfetch_max_streams\fR (uint) | |
430 | .ad | |
431 | .RS 12n | |
432 | Max number of streams per zfetch (prefetch streams per file). | |
433 | .sp | |
434 | Default value: \fB8\fR. | |
435 | .RE | |
436 | ||
437 | .sp | |
438 | .ne 2 | |
439 | .na | |
440 | \fBzfetch_min_sec_reap\fR (uint) | |
441 | .ad | |
442 | .RS 12n | |
443 | Min time before an active prefetch stream can be reclaimed | |
444 | .sp | |
445 | Default value: \fB2\fR. | |
446 | .RE | |
447 | ||
448 | .sp | |
449 | .ne 2 | |
450 | .na | |
451 | \fBzfs_arc_dnode_limit\fR (ulong) | |
452 | .ad | |
453 | .RS 12n | |
454 | When the number of bytes consumed by dnodes in the ARC exceeds this number of | |
455 | bytes, try to unpin some of it in response to demand for non-metadata. This | |
456 | value acts as a ceiling to the amount of dnode metadata, and defaults to 0 which | |
457 | indicates that a percent which is based on \fBzfs_arc_dnode_limit_percent\fR of | |
458 | the ARC meta buffers that may be used for dnodes. | |
459 | ||
460 | See also \fBzfs_arc_meta_prune\fR which serves a similar purpose but is used | |
461 | when the amount of metadata in the ARC exceeds \fBzfs_arc_meta_limit\fR rather | |
462 | than in response to overall demand for non-metadata. | |
463 | ||
464 | .sp | |
465 | Default value: \fB0\fR. | |
466 | .RE | |
467 | ||
468 | .sp | |
469 | .ne 2 | |
470 | .na | |
471 | \fBzfs_arc_dnode_limit_percent\fR (ulong) | |
472 | .ad | |
473 | .RS 12n | |
474 | Percentage that can be consumed by dnodes of ARC meta buffers. | |
475 | .sp | |
476 | See also \fBzfs_arc_dnode_limit\fR which serves a similar purpose but has a | |
477 | higher priority if set to nonzero value. | |
478 | .sp | |
479 | Default value: \fB10\fR%. | |
480 | .RE | |
481 | ||
482 | .sp | |
483 | .ne 2 | |
484 | .na | |
485 | \fBzfs_arc_dnode_reduce_percent\fR (ulong) | |
486 | .ad | |
487 | .RS 12n | |
488 | Percentage of ARC dnodes to try to scan in response to demand for non-metadata | |
489 | when the number of bytes consumed by dnodes exceeds \fBzfs_arc_dnode_limit\fR. | |
490 | ||
491 | .sp | |
492 | Default value: \fB10\fR% of the number of dnodes in the ARC. | |
493 | .RE | |
494 | ||
495 | .sp | |
496 | .ne 2 | |
497 | .na | |
498 | \fBzfs_arc_average_blocksize\fR (int) | |
499 | .ad | |
500 | .RS 12n | |
501 | The ARC's buffer hash table is sized based on the assumption of an average | |
502 | block size of \fBzfs_arc_average_blocksize\fR (default 8K). This works out | |
503 | to roughly 1MB of hash table per 1GB of physical memory with 8-byte pointers. | |
504 | For configurations with a known larger average block size this value can be | |
505 | increased to reduce the memory footprint. | |
506 | ||
507 | .sp | |
508 | Default value: \fB8192\fR. | |
509 | .RE | |
510 | ||
511 | .sp | |
512 | .ne 2 | |
513 | .na | |
514 | \fBzfs_arc_evict_batch_limit\fR (int) | |
515 | .ad | |
516 | .RS 12n | |
517 | Number ARC headers to evict per sub-list before proceeding to another sub-list. | |
518 | This batch-style operation prevents entire sub-lists from being evicted at once | |
519 | but comes at a cost of additional unlocking and locking. | |
520 | .sp | |
521 | Default value: \fB10\fR. | |
522 | .RE | |
523 | ||
524 | .sp | |
525 | .ne 2 | |
526 | .na | |
527 | \fBzfs_arc_grow_retry\fR (int) | |
528 | .ad | |
529 | .RS 12n | |
530 | If set to a non zero value, it will replace the arc_grow_retry value with this value. | |
531 | The arc_grow_retry value (default 5) is the number of seconds the ARC will wait before | |
532 | trying to resume growth after a memory pressure event. | |
533 | .sp | |
534 | Default value: \fB0\fR. | |
535 | .RE | |
536 | ||
537 | .sp | |
538 | .ne 2 | |
539 | .na | |
540 | \fBzfs_arc_lotsfree_percent\fR (int) | |
541 | .ad | |
542 | .RS 12n | |
543 | Throttle I/O when free system memory drops below this percentage of total | |
544 | system memory. Setting this value to 0 will disable the throttle. | |
545 | .sp | |
546 | Default value: \fB10\fR%. | |
547 | .RE | |
548 | ||
549 | .sp | |
550 | .ne 2 | |
551 | .na | |
552 | \fBzfs_arc_max\fR (ulong) | |
553 | .ad | |
554 | .RS 12n | |
555 | Max arc size of ARC in bytes. If set to 0 then it will consume 1/2 of system | |
556 | RAM. This value must be at least 67108864 (64 megabytes). | |
557 | .sp | |
558 | This value can be changed dynamically with some caveats. It cannot be set back | |
559 | to 0 while running and reducing it below the current ARC size will not cause | |
560 | the ARC to shrink without memory pressure to induce shrinking. | |
561 | .sp | |
562 | Default value: \fB0\fR. | |
563 | .RE | |
564 | ||
565 | .sp | |
566 | .ne 2 | |
567 | .na | |
568 | \fBzfs_arc_meta_adjust_restarts\fR (ulong) | |
569 | .ad | |
570 | .RS 12n | |
571 | The number of restart passes to make while scanning the ARC attempting | |
572 | the free buffers in order to stay below the \fBzfs_arc_meta_limit\fR. | |
573 | This value should not need to be tuned but is available to facilitate | |
574 | performance analysis. | |
575 | .sp | |
576 | Default value: \fB4096\fR. | |
577 | .RE | |
578 | ||
579 | .sp | |
580 | .ne 2 | |
581 | .na | |
582 | \fBzfs_arc_meta_limit\fR (ulong) | |
583 | .ad | |
584 | .RS 12n | |
585 | The maximum allowed size in bytes that meta data buffers are allowed to | |
586 | consume in the ARC. When this limit is reached meta data buffers will | |
587 | be reclaimed even if the overall arc_c_max has not been reached. This | |
588 | value defaults to 0 which indicates that a percent which is based on | |
589 | \fBzfs_arc_meta_limit_percent\fR of the ARC may be used for meta data. | |
590 | .sp | |
591 | This value my be changed dynamically except that it cannot be set back to 0 | |
592 | for a specific percent of the ARC; it must be set to an explicit value. | |
593 | .sp | |
594 | Default value: \fB0\fR. | |
595 | .RE | |
596 | ||
597 | .sp | |
598 | .ne 2 | |
599 | .na | |
600 | \fBzfs_arc_meta_limit_percent\fR (ulong) | |
601 | .ad | |
602 | .RS 12n | |
603 | Percentage of ARC buffers that can be used for meta data. | |
604 | ||
605 | See also \fBzfs_arc_meta_limit\fR which serves a similar purpose but has a | |
606 | higher priority if set to nonzero value. | |
607 | ||
608 | .sp | |
609 | Default value: \fB75\fR%. | |
610 | .RE | |
611 | ||
612 | .sp | |
613 | .ne 2 | |
614 | .na | |
615 | \fBzfs_arc_meta_min\fR (ulong) | |
616 | .ad | |
617 | .RS 12n | |
618 | The minimum allowed size in bytes that meta data buffers may consume in | |
619 | the ARC. This value defaults to 0 which disables a floor on the amount | |
620 | of the ARC devoted meta data. | |
621 | .sp | |
622 | Default value: \fB0\fR. | |
623 | .RE | |
624 | ||
625 | .sp | |
626 | .ne 2 | |
627 | .na | |
628 | \fBzfs_arc_meta_prune\fR (int) | |
629 | .ad | |
630 | .RS 12n | |
631 | The number of dentries and inodes to be scanned looking for entries | |
632 | which can be dropped. This may be required when the ARC reaches the | |
633 | \fBzfs_arc_meta_limit\fR because dentries and inodes can pin buffers | |
634 | in the ARC. Increasing this value will cause to dentry and inode caches | |
635 | to be pruned more aggressively. Setting this value to 0 will disable | |
636 | pruning the inode and dentry caches. | |
637 | .sp | |
638 | Default value: \fB10,000\fR. | |
639 | .RE | |
640 | ||
641 | .sp | |
642 | .ne 2 | |
643 | .na | |
644 | \fBzfs_arc_meta_strategy\fR (int) | |
645 | .ad | |
646 | .RS 12n | |
647 | Define the strategy for ARC meta data buffer eviction (meta reclaim strategy). | |
648 | A value of 0 (META_ONLY) will evict only the ARC meta data buffers. | |
649 | A value of 1 (BALANCED) indicates that additional data buffers may be evicted if | |
650 | that is required to in order to evict the required number of meta data buffers. | |
651 | .sp | |
652 | Default value: \fB1\fR. | |
653 | .RE | |
654 | ||
655 | .sp | |
656 | .ne 2 | |
657 | .na | |
658 | \fBzfs_arc_min\fR (ulong) | |
659 | .ad | |
660 | .RS 12n | |
661 | Min arc size of ARC in bytes. If set to 0 then arc_c_min will default to | |
662 | consuming the larger of 32M or 1/32 of total system memory. | |
663 | .sp | |
664 | Default value: \fB0\fR. | |
665 | .RE | |
666 | ||
667 | .sp | |
668 | .ne 2 | |
669 | .na | |
670 | \fBzfs_arc_min_prefetch_ms\fR (int) | |
671 | .ad | |
672 | .RS 12n | |
673 | Minimum time prefetched blocks are locked in the ARC, specified in ms. | |
674 | A value of \fB0\fR will default to 1000 ms. | |
675 | .sp | |
676 | Default value: \fB0\fR. | |
677 | .RE | |
678 | ||
679 | .sp | |
680 | .ne 2 | |
681 | .na | |
682 | \fBzfs_arc_min_prescient_prefetch_ms\fR (int) | |
683 | .ad | |
684 | .RS 12n | |
685 | Minimum time "prescient prefetched" blocks are locked in the ARC, specified | |
686 | in ms. These blocks are meant to be prefetched fairly aggresively ahead of | |
687 | the code that may use them. A value of \fB0\fR will default to 6000 ms. | |
688 | .sp | |
689 | Default value: \fB0\fR. | |
690 | .RE | |
691 | ||
692 | .sp | |
693 | .ne 2 | |
694 | .na | |
695 | \fBzfs_multilist_num_sublists\fR (int) | |
696 | .ad | |
697 | .RS 12n | |
698 | To allow more fine-grained locking, each ARC state contains a series | |
699 | of lists for both data and meta data objects. Locking is performed at | |
700 | the level of these "sub-lists". This parameters controls the number of | |
701 | sub-lists per ARC state, and also applies to other uses of the | |
702 | multilist data structure. | |
703 | .sp | |
704 | Default value: \fB4\fR or the number of online CPUs, whichever is greater | |
705 | .RE | |
706 | ||
707 | .sp | |
708 | .ne 2 | |
709 | .na | |
710 | \fBzfs_arc_overflow_shift\fR (int) | |
711 | .ad | |
712 | .RS 12n | |
713 | The ARC size is considered to be overflowing if it exceeds the current | |
714 | ARC target size (arc_c) by a threshold determined by this parameter. | |
715 | The threshold is calculated as a fraction of arc_c using the formula | |
716 | "arc_c >> \fBzfs_arc_overflow_shift\fR". | |
717 | ||
718 | The default value of 8 causes the ARC to be considered to be overflowing | |
719 | if it exceeds the target size by 1/256th (0.3%) of the target size. | |
720 | ||
721 | When the ARC is overflowing, new buffer allocations are stalled until | |
722 | the reclaim thread catches up and the overflow condition no longer exists. | |
723 | .sp | |
724 | Default value: \fB8\fR. | |
725 | .RE | |
726 | ||
727 | .sp | |
728 | .ne 2 | |
729 | .na | |
730 | ||
731 | \fBzfs_arc_p_min_shift\fR (int) | |
732 | .ad | |
733 | .RS 12n | |
734 | If set to a non zero value, this will update arc_p_min_shift (default 4) | |
735 | with the new value. | |
736 | arc_p_min_shift is used to shift of arc_c for calculating both min and max | |
737 | max arc_p | |
738 | .sp | |
739 | Default value: \fB0\fR. | |
740 | .RE | |
741 | ||
742 | .sp | |
743 | .ne 2 | |
744 | .na | |
745 | \fBzfs_arc_p_dampener_disable\fR (int) | |
746 | .ad | |
747 | .RS 12n | |
748 | Disable arc_p adapt dampener | |
749 | .sp | |
750 | Use \fB1\fR for yes (default) and \fB0\fR to disable. | |
751 | .RE | |
752 | ||
753 | .sp | |
754 | .ne 2 | |
755 | .na | |
756 | \fBzfs_arc_shrink_shift\fR (int) | |
757 | .ad | |
758 | .RS 12n | |
759 | If set to a non zero value, this will update arc_shrink_shift (default 7) | |
760 | with the new value. | |
761 | .sp | |
762 | Default value: \fB0\fR. | |
763 | .RE | |
764 | ||
765 | .sp | |
766 | .ne 2 | |
767 | .na | |
768 | \fBzfs_arc_pc_percent\fR (uint) | |
769 | .ad | |
770 | .RS 12n | |
771 | Percent of pagecache to reclaim arc to | |
772 | ||
773 | This tunable allows ZFS arc to play more nicely with the kernel's LRU | |
774 | pagecache. It can guarantee that the arc size won't collapse under scanning | |
775 | pressure on the pagecache, yet still allows arc to be reclaimed down to | |
776 | zfs_arc_min if necessary. This value is specified as percent of pagecache | |
777 | size (as measured by NR_FILE_PAGES) where that percent may exceed 100. This | |
778 | only operates during memory pressure/reclaim. | |
779 | .sp | |
780 | Default value: \fB0\fR% (disabled). | |
781 | .RE | |
782 | ||
783 | .sp | |
784 | .ne 2 | |
785 | .na | |
786 | \fBzfs_arc_sys_free\fR (ulong) | |
787 | .ad | |
788 | .RS 12n | |
789 | The target number of bytes the ARC should leave as free memory on the system. | |
790 | Defaults to the larger of 1/64 of physical memory or 512K. Setting this | |
791 | option to a non-zero value will override the default. | |
792 | .sp | |
793 | Default value: \fB0\fR. | |
794 | .RE | |
795 | ||
796 | .sp | |
797 | .ne 2 | |
798 | .na | |
799 | \fBzfs_autoimport_disable\fR (int) | |
800 | .ad | |
801 | .RS 12n | |
802 | Disable pool import at module load by ignoring the cache file (typically \fB/etc/zfs/zpool.cache\fR). | |
803 | .sp | |
804 | Use \fB1\fR for yes (default) and \fB0\fR for no. | |
805 | .RE | |
806 | ||
807 | .sp | |
808 | .ne 2 | |
809 | .na | |
810 | \fBzfs_checksums_per_second\fR (int) | |
811 | .ad | |
812 | .RS 12n | |
813 | Rate limit checksum events to this many per second. Note that this should | |
814 | not be set below the zed thresholds (currently 10 checksums over 10 sec) | |
815 | or else zed may not trigger any action. | |
816 | .sp | |
817 | Default value: 20 | |
818 | .RE | |
819 | ||
820 | .sp | |
821 | .ne 2 | |
822 | .na | |
823 | \fBzfs_commit_timeout_pct\fR (int) | |
824 | .ad | |
825 | .RS 12n | |
826 | This controls the amount of time that a ZIL block (lwb) will remain "open" | |
827 | when it isn't "full", and it has a thread waiting for it to be committed to | |
828 | stable storage. The timeout is scaled based on a percentage of the last lwb | |
829 | latency to avoid significantly impacting the latency of each individual | |
830 | transaction record (itx). | |
831 | .sp | |
832 | Default value: \fB5\fR%. | |
833 | .RE | |
834 | ||
835 | .sp | |
836 | .ne 2 | |
837 | .na | |
838 | \fBzfs_dbgmsg_enable\fR (int) | |
839 | .ad | |
840 | .RS 12n | |
841 | Internally ZFS keeps a small log to facilitate debugging. By default the log | |
842 | is disabled, to enable it set this option to 1. The contents of the log can | |
843 | be accessed by reading the /proc/spl/kstat/zfs/dbgmsg file. Writing 0 to | |
844 | this proc file clears the log. | |
845 | .sp | |
846 | Default value: \fB0\fR. | |
847 | .RE | |
848 | ||
849 | .sp | |
850 | .ne 2 | |
851 | .na | |
852 | \fBzfs_dbgmsg_maxsize\fR (int) | |
853 | .ad | |
854 | .RS 12n | |
855 | The maximum size in bytes of the internal ZFS debug log. | |
856 | .sp | |
857 | Default value: \fB4M\fR. | |
858 | .RE | |
859 | ||
860 | .sp | |
861 | .ne 2 | |
862 | .na | |
863 | \fBzfs_dbuf_state_index\fR (int) | |
864 | .ad | |
865 | .RS 12n | |
866 | This feature is currently unused. It is normally used for controlling what | |
867 | reporting is available under /proc/spl/kstat/zfs. | |
868 | .sp | |
869 | Default value: \fB0\fR. | |
870 | .RE | |
871 | ||
872 | .sp | |
873 | .ne 2 | |
874 | .na | |
875 | \fBzfs_deadman_enabled\fR (int) | |
876 | .ad | |
877 | .RS 12n | |
878 | When a pool sync operation takes longer than \fBzfs_deadman_synctime_ms\fR | |
879 | milliseconds, or when an individual I/O takes longer than | |
880 | \fBzfs_deadman_ziotime_ms\fR milliseconds, then the operation is considered to | |
881 | be "hung". If \fBzfs_deadman_enabled\fR is set then the deadman behavior is | |
882 | invoked as described by the \fBzfs_deadman_failmode\fR module option. | |
883 | By default the deadman is enabled and configured to \fBwait\fR which results | |
884 | in "hung" I/Os only being logged. The deadman is automatically disabled | |
885 | when a pool gets suspended. | |
886 | .sp | |
887 | Default value: \fB1\fR. | |
888 | .RE | |
889 | ||
890 | .sp | |
891 | .ne 2 | |
892 | .na | |
893 | \fBzfs_deadman_failmode\fR (charp) | |
894 | .ad | |
895 | .RS 12n | |
896 | Controls the failure behavior when the deadman detects a "hung" I/O. Valid | |
897 | values are \fBwait\fR, \fBcontinue\fR, and \fBpanic\fR. | |
898 | .sp | |
899 | \fBwait\fR - Wait for a "hung" I/O to complete. For each "hung" I/O a | |
900 | "deadman" event will be posted describing that I/O. | |
901 | .sp | |
902 | \fBcontinue\fR - Attempt to recover from a "hung" I/O by re-dispatching it | |
903 | to the I/O pipeline if possible. | |
904 | .sp | |
905 | \fBpanic\fR - Panic the system. This can be used to facilitate an automatic | |
906 | fail-over to a properly configured fail-over partner. | |
907 | .sp | |
908 | Default value: \fBwait\fR. | |
909 | .RE | |
910 | ||
911 | .sp | |
912 | .ne 2 | |
913 | .na | |
914 | \fBzfs_deadman_checktime_ms\fR (int) | |
915 | .ad | |
916 | .RS 12n | |
917 | Check time in milliseconds. This defines the frequency at which we check | |
918 | for hung I/O and potentially invoke the \fBzfs_deadman_failmode\fR behavior. | |
919 | .sp | |
920 | Default value: \fB60,000\fR. | |
921 | .RE | |
922 | ||
923 | .sp | |
924 | .ne 2 | |
925 | .na | |
926 | \fBzfs_deadman_synctime_ms\fR (ulong) | |
927 | .ad | |
928 | .RS 12n | |
929 | Interval in milliseconds after which the deadman is triggered and also | |
930 | the interval after which a pool sync operation is considered to be "hung". | |
931 | Once this limit is exceeded the deadman will be invoked every | |
932 | \fBzfs_deadman_checktime_ms\fR milliseconds until the pool sync completes. | |
933 | .sp | |
934 | Default value: \fB600,000\fR. | |
935 | .RE | |
936 | ||
937 | .sp | |
938 | .ne 2 | |
939 | .na | |
940 | \fBzfs_deadman_ziotime_ms\fR (ulong) | |
941 | .ad | |
942 | .RS 12n | |
943 | Interval in milliseconds after which the deadman is triggered and an | |
944 | individual IO operation is considered to be "hung". As long as the I/O | |
945 | remains "hung" the deadman will be invoked every \fBzfs_deadman_checktime_ms\fR | |
946 | milliseconds until the I/O completes. | |
947 | .sp | |
948 | Default value: \fB300,000\fR. | |
949 | .RE | |
950 | ||
951 | .sp | |
952 | .ne 2 | |
953 | .na | |
954 | \fBzfs_dedup_prefetch\fR (int) | |
955 | .ad | |
956 | .RS 12n | |
957 | Enable prefetching dedup-ed blks | |
958 | .sp | |
959 | Use \fB1\fR for yes and \fB0\fR to disable (default). | |
960 | .RE | |
961 | ||
962 | .sp | |
963 | .ne 2 | |
964 | .na | |
965 | \fBzfs_delay_min_dirty_percent\fR (int) | |
966 | .ad | |
967 | .RS 12n | |
968 | Start to delay each transaction once there is this amount of dirty data, | |
969 | expressed as a percentage of \fBzfs_dirty_data_max\fR. | |
970 | This value should be >= zfs_vdev_async_write_active_max_dirty_percent. | |
971 | See the section "ZFS TRANSACTION DELAY". | |
972 | .sp | |
973 | Default value: \fB60\fR%. | |
974 | .RE | |
975 | ||
976 | .sp | |
977 | .ne 2 | |
978 | .na | |
979 | \fBzfs_delay_scale\fR (int) | |
980 | .ad | |
981 | .RS 12n | |
982 | This controls how quickly the transaction delay approaches infinity. | |
983 | Larger values cause longer delays for a given amount of dirty data. | |
984 | .sp | |
985 | For the smoothest delay, this value should be about 1 billion divided | |
986 | by the maximum number of operations per second. This will smoothly | |
987 | handle between 10x and 1/10th this number. | |
988 | .sp | |
989 | See the section "ZFS TRANSACTION DELAY". | |
990 | .sp | |
991 | Note: \fBzfs_delay_scale\fR * \fBzfs_dirty_data_max\fR must be < 2^64. | |
992 | .sp | |
993 | Default value: \fB500,000\fR. | |
994 | .RE | |
995 | ||
996 | .sp | |
997 | .ne 2 | |
998 | .na | |
999 | \fBzfs_delays_per_second\fR (int) | |
1000 | .ad | |
1001 | .RS 12n | |
1002 | Rate limit IO delay events to this many per second. | |
1003 | .sp | |
1004 | Default value: 20 | |
1005 | .RE | |
1006 | ||
1007 | .sp | |
1008 | .ne 2 | |
1009 | .na | |
1010 | \fBzfs_delete_blocks\fR (ulong) | |
1011 | .ad | |
1012 | .RS 12n | |
1013 | This is the used to define a large file for the purposes of delete. Files | |
1014 | containing more than \fBzfs_delete_blocks\fR will be deleted asynchronously | |
1015 | while smaller files are deleted synchronously. Decreasing this value will | |
1016 | reduce the time spent in an unlink(2) system call at the expense of a longer | |
1017 | delay before the freed space is available. | |
1018 | .sp | |
1019 | Default value: \fB20,480\fR. | |
1020 | .RE | |
1021 | ||
1022 | .sp | |
1023 | .ne 2 | |
1024 | .na | |
1025 | \fBzfs_dirty_data_max\fR (int) | |
1026 | .ad | |
1027 | .RS 12n | |
1028 | Determines the dirty space limit in bytes. Once this limit is exceeded, new | |
1029 | writes are halted until space frees up. This parameter takes precedence | |
1030 | over \fBzfs_dirty_data_max_percent\fR. | |
1031 | See the section "ZFS TRANSACTION DELAY". | |
1032 | .sp | |
1033 | Default value: \fB10\fR% of physical RAM, capped at \fBzfs_dirty_data_max_max\fR. | |
1034 | .RE | |
1035 | ||
1036 | .sp | |
1037 | .ne 2 | |
1038 | .na | |
1039 | \fBzfs_dirty_data_max_max\fR (int) | |
1040 | .ad | |
1041 | .RS 12n | |
1042 | Maximum allowable value of \fBzfs_dirty_data_max\fR, expressed in bytes. | |
1043 | This limit is only enforced at module load time, and will be ignored if | |
1044 | \fBzfs_dirty_data_max\fR is later changed. This parameter takes | |
1045 | precedence over \fBzfs_dirty_data_max_max_percent\fR. See the section | |
1046 | "ZFS TRANSACTION DELAY". | |
1047 | .sp | |
1048 | Default value: \fB25\fR% of physical RAM. | |
1049 | .RE | |
1050 | ||
1051 | .sp | |
1052 | .ne 2 | |
1053 | .na | |
1054 | \fBzfs_dirty_data_max_max_percent\fR (int) | |
1055 | .ad | |
1056 | .RS 12n | |
1057 | Maximum allowable value of \fBzfs_dirty_data_max\fR, expressed as a | |
1058 | percentage of physical RAM. This limit is only enforced at module load | |
1059 | time, and will be ignored if \fBzfs_dirty_data_max\fR is later changed. | |
1060 | The parameter \fBzfs_dirty_data_max_max\fR takes precedence over this | |
1061 | one. See the section "ZFS TRANSACTION DELAY". | |
1062 | .sp | |
1063 | Default value: \fB25\fR%. | |
1064 | .RE | |
1065 | ||
1066 | .sp | |
1067 | .ne 2 | |
1068 | .na | |
1069 | \fBzfs_dirty_data_max_percent\fR (int) | |
1070 | .ad | |
1071 | .RS 12n | |
1072 | Determines the dirty space limit, expressed as a percentage of all | |
1073 | memory. Once this limit is exceeded, new writes are halted until space frees | |
1074 | up. The parameter \fBzfs_dirty_data_max\fR takes precedence over this | |
1075 | one. See the section "ZFS TRANSACTION DELAY". | |
1076 | .sp | |
1077 | Default value: \fB10\fR%, subject to \fBzfs_dirty_data_max_max\fR. | |
1078 | .RE | |
1079 | ||
1080 | .sp | |
1081 | .ne 2 | |
1082 | .na | |
1083 | \fBzfs_dirty_data_sync\fR (int) | |
1084 | .ad | |
1085 | .RS 12n | |
1086 | Start syncing out a transaction group if there is at least this much dirty data. | |
1087 | .sp | |
1088 | Default value: \fB67,108,864\fR. | |
1089 | .RE | |
1090 | ||
1091 | .sp | |
1092 | .ne 2 | |
1093 | .na | |
1094 | \fBzfs_fletcher_4_impl\fR (string) | |
1095 | .ad | |
1096 | .RS 12n | |
1097 | Select a fletcher 4 implementation. | |
1098 | .sp | |
1099 | Supported selectors are: \fBfastest\fR, \fBscalar\fR, \fBsse2\fR, \fBssse3\fR, | |
1100 | \fBavx2\fR, \fBavx512f\fR, and \fBaarch64_neon\fR. | |
1101 | All of the selectors except \fBfastest\fR and \fBscalar\fR require instruction | |
1102 | set extensions to be available and will only appear if ZFS detects that they are | |
1103 | present at runtime. If multiple implementations of fletcher 4 are available, | |
1104 | the \fBfastest\fR will be chosen using a micro benchmark. Selecting \fBscalar\fR | |
1105 | results in the original, CPU based calculation, being used. Selecting any option | |
1106 | other than \fBfastest\fR and \fBscalar\fR results in vector instructions from | |
1107 | the respective CPU instruction set being used. | |
1108 | .sp | |
1109 | Default value: \fBfastest\fR. | |
1110 | .RE | |
1111 | ||
1112 | .sp | |
1113 | .ne 2 | |
1114 | .na | |
1115 | \fBzfs_free_bpobj_enabled\fR (int) | |
1116 | .ad | |
1117 | .RS 12n | |
1118 | Enable/disable the processing of the free_bpobj object. | |
1119 | .sp | |
1120 | Default value: \fB1\fR. | |
1121 | .RE | |
1122 | ||
1123 | .sp | |
1124 | .ne 2 | |
1125 | .na | |
1126 | \fBzfs_free_max_blocks\fR (ulong) | |
1127 | .ad | |
1128 | .RS 12n | |
1129 | Maximum number of blocks freed in a single txg. | |
1130 | .sp | |
1131 | Default value: \fB100,000\fR. | |
1132 | .RE | |
1133 | ||
1134 | .sp | |
1135 | .ne 2 | |
1136 | .na | |
1137 | \fBzfs_vdev_async_read_max_active\fR (int) | |
1138 | .ad | |
1139 | .RS 12n | |
1140 | Maximum asynchronous read I/Os active to each device. | |
1141 | See the section "ZFS I/O SCHEDULER". | |
1142 | .sp | |
1143 | Default value: \fB3\fR. | |
1144 | .RE | |
1145 | ||
1146 | .sp | |
1147 | .ne 2 | |
1148 | .na | |
1149 | \fBzfs_vdev_async_read_min_active\fR (int) | |
1150 | .ad | |
1151 | .RS 12n | |
1152 | Minimum asynchronous read I/Os active to each device. | |
1153 | See the section "ZFS I/O SCHEDULER". | |
1154 | .sp | |
1155 | Default value: \fB1\fR. | |
1156 | .RE | |
1157 | ||
1158 | .sp | |
1159 | .ne 2 | |
1160 | .na | |
1161 | \fBzfs_vdev_async_write_active_max_dirty_percent\fR (int) | |
1162 | .ad | |
1163 | .RS 12n | |
1164 | When the pool has more than | |
1165 | \fBzfs_vdev_async_write_active_max_dirty_percent\fR dirty data, use | |
1166 | \fBzfs_vdev_async_write_max_active\fR to limit active async writes. If | |
1167 | the dirty data is between min and max, the active I/O limit is linearly | |
1168 | interpolated. See the section "ZFS I/O SCHEDULER". | |
1169 | .sp | |
1170 | Default value: \fB60\fR%. | |
1171 | .RE | |
1172 | ||
1173 | .sp | |
1174 | .ne 2 | |
1175 | .na | |
1176 | \fBzfs_vdev_async_write_active_min_dirty_percent\fR (int) | |
1177 | .ad | |
1178 | .RS 12n | |
1179 | When the pool has less than | |
1180 | \fBzfs_vdev_async_write_active_min_dirty_percent\fR dirty data, use | |
1181 | \fBzfs_vdev_async_write_min_active\fR to limit active async writes. If | |
1182 | the dirty data is between min and max, the active I/O limit is linearly | |
1183 | interpolated. See the section "ZFS I/O SCHEDULER". | |
1184 | .sp | |
1185 | Default value: \fB30\fR%. | |
1186 | .RE | |
1187 | ||
1188 | .sp | |
1189 | .ne 2 | |
1190 | .na | |
1191 | \fBzfs_vdev_async_write_max_active\fR (int) | |
1192 | .ad | |
1193 | .RS 12n | |
1194 | Maximum asynchronous write I/Os active to each device. | |
1195 | See the section "ZFS I/O SCHEDULER". | |
1196 | .sp | |
1197 | Default value: \fB10\fR. | |
1198 | .RE | |
1199 | ||
1200 | .sp | |
1201 | .ne 2 | |
1202 | .na | |
1203 | \fBzfs_vdev_async_write_min_active\fR (int) | |
1204 | .ad | |
1205 | .RS 12n | |
1206 | Minimum asynchronous write I/Os active to each device. | |
1207 | See the section "ZFS I/O SCHEDULER". | |
1208 | .sp | |
1209 | Lower values are associated with better latency on rotational media but poorer | |
1210 | resilver performance. The default value of 2 was chosen as a compromise. A | |
1211 | value of 3 has been shown to improve resilver performance further at a cost of | |
1212 | further increasing latency. | |
1213 | .sp | |
1214 | Default value: \fB2\fR. | |
1215 | .RE | |
1216 | ||
1217 | .sp | |
1218 | .ne 2 | |
1219 | .na | |
1220 | \fBzfs_vdev_max_active\fR (int) | |
1221 | .ad | |
1222 | .RS 12n | |
1223 | The maximum number of I/Os active to each device. Ideally, this will be >= | |
1224 | the sum of each queue's max_active. It must be at least the sum of each | |
1225 | queue's min_active. See the section "ZFS I/O SCHEDULER". | |
1226 | .sp | |
1227 | Default value: \fB1,000\fR. | |
1228 | .RE | |
1229 | ||
1230 | .sp | |
1231 | .ne 2 | |
1232 | .na | |
1233 | \fBzfs_vdev_scrub_max_active\fR (int) | |
1234 | .ad | |
1235 | .RS 12n | |
1236 | Maximum scrub I/Os active to each device. | |
1237 | See the section "ZFS I/O SCHEDULER". | |
1238 | .sp | |
1239 | Default value: \fB2\fR. | |
1240 | .RE | |
1241 | ||
1242 | .sp | |
1243 | .ne 2 | |
1244 | .na | |
1245 | \fBzfs_vdev_scrub_min_active\fR (int) | |
1246 | .ad | |
1247 | .RS 12n | |
1248 | Minimum scrub I/Os active to each device. | |
1249 | See the section "ZFS I/O SCHEDULER". | |
1250 | .sp | |
1251 | Default value: \fB1\fR. | |
1252 | .RE | |
1253 | ||
1254 | .sp | |
1255 | .ne 2 | |
1256 | .na | |
1257 | \fBzfs_vdev_sync_read_max_active\fR (int) | |
1258 | .ad | |
1259 | .RS 12n | |
1260 | Maximum synchronous read I/Os active to each device. | |
1261 | See the section "ZFS I/O SCHEDULER". | |
1262 | .sp | |
1263 | Default value: \fB10\fR. | |
1264 | .RE | |
1265 | ||
1266 | .sp | |
1267 | .ne 2 | |
1268 | .na | |
1269 | \fBzfs_vdev_sync_read_min_active\fR (int) | |
1270 | .ad | |
1271 | .RS 12n | |
1272 | Minimum synchronous read I/Os active to each device. | |
1273 | See the section "ZFS I/O SCHEDULER". | |
1274 | .sp | |
1275 | Default value: \fB10\fR. | |
1276 | .RE | |
1277 | ||
1278 | .sp | |
1279 | .ne 2 | |
1280 | .na | |
1281 | \fBzfs_vdev_sync_write_max_active\fR (int) | |
1282 | .ad | |
1283 | .RS 12n | |
1284 | Maximum synchronous write I/Os active to each device. | |
1285 | See the section "ZFS I/O SCHEDULER". | |
1286 | .sp | |
1287 | Default value: \fB10\fR. | |
1288 | .RE | |
1289 | ||
1290 | .sp | |
1291 | .ne 2 | |
1292 | .na | |
1293 | \fBzfs_vdev_sync_write_min_active\fR (int) | |
1294 | .ad | |
1295 | .RS 12n | |
1296 | Minimum synchronous write I/Os active to each device. | |
1297 | See the section "ZFS I/O SCHEDULER". | |
1298 | .sp | |
1299 | Default value: \fB10\fR. | |
1300 | .RE | |
1301 | ||
1302 | .sp | |
1303 | .ne 2 | |
1304 | .na | |
1305 | \fBzfs_vdev_queue_depth_pct\fR (int) | |
1306 | .ad | |
1307 | .RS 12n | |
1308 | Maximum number of queued allocations per top-level vdev expressed as | |
1309 | a percentage of \fBzfs_vdev_async_write_max_active\fR which allows the | |
1310 | system to detect devices that are more capable of handling allocations | |
1311 | and to allocate more blocks to those devices. It allows for dynamic | |
1312 | allocation distribution when devices are imbalanced as fuller devices | |
1313 | will tend to be slower than empty devices. | |
1314 | ||
1315 | See also \fBzio_dva_throttle_enabled\fR. | |
1316 | .sp | |
1317 | Default value: \fB1000\fR%. | |
1318 | .RE | |
1319 | ||
1320 | .sp | |
1321 | .ne 2 | |
1322 | .na | |
1323 | \fBzfs_expire_snapshot\fR (int) | |
1324 | .ad | |
1325 | .RS 12n | |
1326 | Seconds to expire .zfs/snapshot | |
1327 | .sp | |
1328 | Default value: \fB300\fR. | |
1329 | .RE | |
1330 | ||
1331 | .sp | |
1332 | .ne 2 | |
1333 | .na | |
1334 | \fBzfs_admin_snapshot\fR (int) | |
1335 | .ad | |
1336 | .RS 12n | |
1337 | Allow the creation, removal, or renaming of entries in the .zfs/snapshot | |
1338 | directory to cause the creation, destruction, or renaming of snapshots. | |
1339 | When enabled this functionality works both locally and over NFS exports | |
1340 | which have the 'no_root_squash' option set. This functionality is disabled | |
1341 | by default. | |
1342 | .sp | |
1343 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
1344 | .RE | |
1345 | ||
1346 | .sp | |
1347 | .ne 2 | |
1348 | .na | |
1349 | \fBzfs_flags\fR (int) | |
1350 | .ad | |
1351 | .RS 12n | |
1352 | Set additional debugging flags. The following flags may be bitwise-or'd | |
1353 | together. | |
1354 | .sp | |
1355 | .TS | |
1356 | box; | |
1357 | rB lB | |
1358 | lB lB | |
1359 | r l. | |
1360 | Value Symbolic Name | |
1361 | Description | |
1362 | _ | |
1363 | 1 ZFS_DEBUG_DPRINTF | |
1364 | Enable dprintf entries in the debug log. | |
1365 | _ | |
1366 | 2 ZFS_DEBUG_DBUF_VERIFY * | |
1367 | Enable extra dbuf verifications. | |
1368 | _ | |
1369 | 4 ZFS_DEBUG_DNODE_VERIFY * | |
1370 | Enable extra dnode verifications. | |
1371 | _ | |
1372 | 8 ZFS_DEBUG_SNAPNAMES | |
1373 | Enable snapshot name verification. | |
1374 | _ | |
1375 | 16 ZFS_DEBUG_MODIFY | |
1376 | Check for illegally modified ARC buffers. | |
1377 | _ | |
1378 | 32 ZFS_DEBUG_SPA | |
1379 | Enable spa_dbgmsg entries in the debug log. | |
1380 | _ | |
1381 | 64 ZFS_DEBUG_ZIO_FREE | |
1382 | Enable verification of block frees. | |
1383 | _ | |
1384 | 128 ZFS_DEBUG_HISTOGRAM_VERIFY | |
1385 | Enable extra spacemap histogram verifications. | |
1386 | _ | |
1387 | 256 ZFS_DEBUG_METASLAB_VERIFY | |
1388 | Verify space accounting on disk matches in-core range_trees. | |
1389 | _ | |
1390 | 512 ZFS_DEBUG_SET_ERROR | |
1391 | Enable SET_ERROR and dprintf entries in the debug log. | |
1392 | .TE | |
1393 | .sp | |
1394 | * Requires debug build. | |
1395 | .sp | |
1396 | Default value: \fB0\fR. | |
1397 | .RE | |
1398 | ||
1399 | .sp | |
1400 | .ne 2 | |
1401 | .na | |
1402 | \fBzfs_free_leak_on_eio\fR (int) | |
1403 | .ad | |
1404 | .RS 12n | |
1405 | If destroy encounters an EIO while reading metadata (e.g. indirect | |
1406 | blocks), space referenced by the missing metadata can not be freed. | |
1407 | Normally this causes the background destroy to become "stalled", as | |
1408 | it is unable to make forward progress. While in this stalled state, | |
1409 | all remaining space to free from the error-encountering filesystem is | |
1410 | "temporarily leaked". Set this flag to cause it to ignore the EIO, | |
1411 | permanently leak the space from indirect blocks that can not be read, | |
1412 | and continue to free everything else that it can. | |
1413 | ||
1414 | The default, "stalling" behavior is useful if the storage partially | |
1415 | fails (i.e. some but not all i/os fail), and then later recovers. In | |
1416 | this case, we will be able to continue pool operations while it is | |
1417 | partially failed, and when it recovers, we can continue to free the | |
1418 | space, with no leaks. However, note that this case is actually | |
1419 | fairly rare. | |
1420 | ||
1421 | Typically pools either (a) fail completely (but perhaps temporarily, | |
1422 | e.g. a top-level vdev going offline), or (b) have localized, | |
1423 | permanent errors (e.g. disk returns the wrong data due to bit flip or | |
1424 | firmware bug). In case (a), this setting does not matter because the | |
1425 | pool will be suspended and the sync thread will not be able to make | |
1426 | forward progress regardless. In case (b), because the error is | |
1427 | permanent, the best we can do is leak the minimum amount of space, | |
1428 | which is what setting this flag will do. Therefore, it is reasonable | |
1429 | for this flag to normally be set, but we chose the more conservative | |
1430 | approach of not setting it, so that there is no possibility of | |
1431 | leaking space in the "partial temporary" failure case. | |
1432 | .sp | |
1433 | Default value: \fB0\fR. | |
1434 | .RE | |
1435 | ||
1436 | .sp | |
1437 | .ne 2 | |
1438 | .na | |
1439 | \fBzfs_free_min_time_ms\fR (int) | |
1440 | .ad | |
1441 | .RS 12n | |
1442 | During a \fBzfs destroy\fR operation using \fBfeature@async_destroy\fR a minimum | |
1443 | of this much time will be spent working on freeing blocks per txg. | |
1444 | .sp | |
1445 | Default value: \fB1,000\fR. | |
1446 | .RE | |
1447 | ||
1448 | .sp | |
1449 | .ne 2 | |
1450 | .na | |
1451 | \fBzfs_immediate_write_sz\fR (long) | |
1452 | .ad | |
1453 | .RS 12n | |
1454 | Largest data block to write to zil. Larger blocks will be treated as if the | |
1455 | dataset being written to had the property setting \fBlogbias=throughput\fR. | |
1456 | .sp | |
1457 | Default value: \fB32,768\fR. | |
1458 | .RE | |
1459 | ||
1460 | .sp | |
1461 | .ne 2 | |
1462 | .na | |
1463 | \fBzfs_max_recordsize\fR (int) | |
1464 | .ad | |
1465 | .RS 12n | |
1466 | We currently support block sizes from 512 bytes to 16MB. The benefits of | |
1467 | larger blocks, and thus larger IO, need to be weighed against the cost of | |
1468 | COWing a giant block to modify one byte. Additionally, very large blocks | |
1469 | can have an impact on i/o latency, and also potentially on the memory | |
1470 | allocator. Therefore, we do not allow the recordsize to be set larger than | |
1471 | zfs_max_recordsize (default 1MB). Larger blocks can be created by changing | |
1472 | this tunable, and pools with larger blocks can always be imported and used, | |
1473 | regardless of this setting. | |
1474 | .sp | |
1475 | Default value: \fB1,048,576\fR. | |
1476 | .RE | |
1477 | ||
1478 | .sp | |
1479 | .ne 2 | |
1480 | .na | |
1481 | \fBzfs_metaslab_fragmentation_threshold\fR (int) | |
1482 | .ad | |
1483 | .RS 12n | |
1484 | Allow metaslabs to keep their active state as long as their fragmentation | |
1485 | percentage is less than or equal to this value. An active metaslab that | |
1486 | exceeds this threshold will no longer keep its active status allowing | |
1487 | better metaslabs to be selected. | |
1488 | .sp | |
1489 | Default value: \fB70\fR. | |
1490 | .RE | |
1491 | ||
1492 | .sp | |
1493 | .ne 2 | |
1494 | .na | |
1495 | \fBzfs_mg_fragmentation_threshold\fR (int) | |
1496 | .ad | |
1497 | .RS 12n | |
1498 | Metaslab groups are considered eligible for allocations if their | |
1499 | fragmentation metric (measured as a percentage) is less than or equal to | |
1500 | this value. If a metaslab group exceeds this threshold then it will be | |
1501 | skipped unless all metaslab groups within the metaslab class have also | |
1502 | crossed this threshold. | |
1503 | .sp | |
1504 | Default value: \fB85\fR. | |
1505 | .RE | |
1506 | ||
1507 | .sp | |
1508 | .ne 2 | |
1509 | .na | |
1510 | \fBzfs_mg_noalloc_threshold\fR (int) | |
1511 | .ad | |
1512 | .RS 12n | |
1513 | Defines a threshold at which metaslab groups should be eligible for | |
1514 | allocations. The value is expressed as a percentage of free space | |
1515 | beyond which a metaslab group is always eligible for allocations. | |
1516 | If a metaslab group's free space is less than or equal to the | |
1517 | threshold, the allocator will avoid allocating to that group | |
1518 | unless all groups in the pool have reached the threshold. Once all | |
1519 | groups have reached the threshold, all groups are allowed to accept | |
1520 | allocations. The default value of 0 disables the feature and causes | |
1521 | all metaslab groups to be eligible for allocations. | |
1522 | ||
1523 | This parameter allows one to deal with pools having heavily imbalanced | |
1524 | vdevs such as would be the case when a new vdev has been added. | |
1525 | Setting the threshold to a non-zero percentage will stop allocations | |
1526 | from being made to vdevs that aren't filled to the specified percentage | |
1527 | and allow lesser filled vdevs to acquire more allocations than they | |
1528 | otherwise would under the old \fBzfs_mg_alloc_failures\fR facility. | |
1529 | .sp | |
1530 | Default value: \fB0\fR. | |
1531 | .RE | |
1532 | ||
1533 | .sp | |
1534 | .ne 2 | |
1535 | .na | |
1536 | \fBzfs_multihost_history\fR (int) | |
1537 | .ad | |
1538 | .RS 12n | |
1539 | Historical statistics for the last N multihost updates will be available in | |
1540 | \fB/proc/spl/kstat/zfs/<pool>/multihost\fR | |
1541 | .sp | |
1542 | Default value: \fB0\fR. | |
1543 | .RE | |
1544 | ||
1545 | .sp | |
1546 | .ne 2 | |
1547 | .na | |
1548 | \fBzfs_multihost_interval\fR (ulong) | |
1549 | .ad | |
1550 | .RS 12n | |
1551 | Used to control the frequency of multihost writes which are performed when the | |
1552 | \fBmultihost\fR pool property is on. This is one factor used to determine | |
1553 | the length of the activity check during import. | |
1554 | .sp | |
1555 | The multihost write period is \fBzfs_multihost_interval / leaf-vdevs\fR milliseconds. | |
1556 | This means that on average a multihost write will be issued for each leaf vdev every | |
1557 | \fBzfs_multihost_interval\fR milliseconds. In practice, the observed period can | |
1558 | vary with the I/O load and this observed value is the delay which is stored in | |
1559 | the uberblock. | |
1560 | .sp | |
1561 | On import the activity check waits a minimum amount of time determined by | |
1562 | \fBzfs_multihost_interval * zfs_multihost_import_intervals\fR. The activity | |
1563 | check time may be further extended if the value of mmp delay found in the best | |
1564 | uberblock indicates actual multihost updates happened at longer intervals than | |
1565 | \fBzfs_multihost_interval\fR. A minimum value of \fB100ms\fR is enforced. | |
1566 | .sp | |
1567 | Default value: \fB1000\fR. | |
1568 | .RE | |
1569 | ||
1570 | .sp | |
1571 | .ne 2 | |
1572 | .na | |
1573 | \fBzfs_multihost_import_intervals\fR (uint) | |
1574 | .ad | |
1575 | .RS 12n | |
1576 | Used to control the duration of the activity test on import. Smaller values of | |
1577 | \fBzfs_multihost_import_intervals\fR will reduce the import time but increase | |
1578 | the risk of failing to detect an active pool. The total activity check time is | |
1579 | never allowed to drop below one second. A value of 0 is ignored and treated as | |
1580 | if it was set to 1 | |
1581 | .sp | |
1582 | Default value: \fB10\fR. | |
1583 | .RE | |
1584 | ||
1585 | .sp | |
1586 | .ne 2 | |
1587 | .na | |
1588 | \fBzfs_multihost_fail_intervals\fR (uint) | |
1589 | .ad | |
1590 | .RS 12n | |
1591 | Controls the behavior of the pool when multihost write failures are detected. | |
1592 | .sp | |
1593 | When \fBzfs_multihost_fail_intervals = 0\fR then multihost write failures are ignored. | |
1594 | The failures will still be reported to the ZED which depending on its | |
1595 | configuration may take action such as suspending the pool or offlining a device. | |
1596 | .sp | |
1597 | When \fBzfs_multihost_fail_intervals > 0\fR then sequential multihost write failures | |
1598 | will cause the pool to be suspended. This occurs when | |
1599 | \fBzfs_multihost_fail_intervals * zfs_multihost_interval\fR milliseconds have | |
1600 | passed since the last successful multihost write. This guarantees the activity test | |
1601 | will see multihost writes if the pool is imported. | |
1602 | .sp | |
1603 | Default value: \fB5\fR. | |
1604 | .RE | |
1605 | ||
1606 | .sp | |
1607 | .ne 2 | |
1608 | .na | |
1609 | \fBzfs_no_scrub_io\fR (int) | |
1610 | .ad | |
1611 | .RS 12n | |
1612 | Set for no scrub I/O. This results in scrubs not actually scrubbing data and | |
1613 | simply doing a metadata crawl of the pool instead. | |
1614 | .sp | |
1615 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
1616 | .RE | |
1617 | ||
1618 | .sp | |
1619 | .ne 2 | |
1620 | .na | |
1621 | \fBzfs_no_scrub_prefetch\fR (int) | |
1622 | .ad | |
1623 | .RS 12n | |
1624 | Set to disable block prefetching for scrubs. | |
1625 | .sp | |
1626 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
1627 | .RE | |
1628 | ||
1629 | .sp | |
1630 | .ne 2 | |
1631 | .na | |
1632 | \fBzfs_nocacheflush\fR (int) | |
1633 | .ad | |
1634 | .RS 12n | |
1635 | Disable cache flush operations on disks when writing. Beware, this may cause | |
1636 | corruption if disks re-order writes. | |
1637 | .sp | |
1638 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
1639 | .RE | |
1640 | ||
1641 | .sp | |
1642 | .ne 2 | |
1643 | .na | |
1644 | \fBzfs_nopwrite_enabled\fR (int) | |
1645 | .ad | |
1646 | .RS 12n | |
1647 | Enable NOP writes | |
1648 | .sp | |
1649 | Use \fB1\fR for yes (default) and \fB0\fR to disable. | |
1650 | .RE | |
1651 | ||
1652 | .sp | |
1653 | .ne 2 | |
1654 | .na | |
1655 | \fBzfs_dmu_offset_next_sync\fR (int) | |
1656 | .ad | |
1657 | .RS 12n | |
1658 | Enable forcing txg sync to find holes. When enabled forces ZFS to act | |
1659 | like prior versions when SEEK_HOLE or SEEK_DATA flags are used, which | |
1660 | when a dnode is dirty causes txg's to be synced so that this data can be | |
1661 | found. | |
1662 | .sp | |
1663 | Use \fB1\fR for yes and \fB0\fR to disable (default). | |
1664 | .RE | |
1665 | ||
1666 | .sp | |
1667 | .ne 2 | |
1668 | .na | |
1669 | \fBzfs_pd_bytes_max\fR (int) | |
1670 | .ad | |
1671 | .RS 12n | |
1672 | The number of bytes which should be prefetched during a pool traversal | |
1673 | (eg: \fBzfs send\fR or other data crawling operations) | |
1674 | .sp | |
1675 | Default value: \fB52,428,800\fR. | |
1676 | .RE | |
1677 | ||
1678 | .sp | |
1679 | .ne 2 | |
1680 | .na | |
1681 | \fBzfs_per_txg_dirty_frees_percent \fR (ulong) | |
1682 | .ad | |
1683 | .RS 12n | |
1684 | Tunable to control percentage of dirtied blocks from frees in one TXG. | |
1685 | After this threshold is crossed, additional dirty blocks from frees | |
1686 | wait until the next TXG. | |
1687 | A value of zero will disable this throttle. | |
1688 | .sp | |
1689 | Default value: \fB30\fR and \fB0\fR to disable. | |
1690 | .RE | |
1691 | ||
1692 | ||
1693 | ||
1694 | .sp | |
1695 | .ne 2 | |
1696 | .na | |
1697 | \fBzfs_prefetch_disable\fR (int) | |
1698 | .ad | |
1699 | .RS 12n | |
1700 | This tunable disables predictive prefetch. Note that it leaves "prescient" | |
1701 | prefetch (e.g. prefetch for zfs send) intact. Unlike predictive prefetch, | |
1702 | prescient prefetch never issues i/os that end up not being needed, so it | |
1703 | can't hurt performance. | |
1704 | .sp | |
1705 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
1706 | .RE | |
1707 | ||
1708 | .sp | |
1709 | .ne 2 | |
1710 | .na | |
1711 | \fBzfs_read_chunk_size\fR (long) | |
1712 | .ad | |
1713 | .RS 12n | |
1714 | Bytes to read per chunk | |
1715 | .sp | |
1716 | Default value: \fB1,048,576\fR. | |
1717 | .RE | |
1718 | ||
1719 | .sp | |
1720 | .ne 2 | |
1721 | .na | |
1722 | \fBzfs_read_history\fR (int) | |
1723 | .ad | |
1724 | .RS 12n | |
1725 | Historical statistics for the last N reads will be available in | |
1726 | \fB/proc/spl/kstat/zfs/<pool>/reads\fR | |
1727 | .sp | |
1728 | Default value: \fB0\fR (no data is kept). | |
1729 | .RE | |
1730 | ||
1731 | .sp | |
1732 | .ne 2 | |
1733 | .na | |
1734 | \fBzfs_read_history_hits\fR (int) | |
1735 | .ad | |
1736 | .RS 12n | |
1737 | Include cache hits in read history | |
1738 | .sp | |
1739 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
1740 | .RE | |
1741 | ||
1742 | .sp | |
1743 | .ne 2 | |
1744 | .na | |
1745 | \fBzfs_recover\fR (int) | |
1746 | .ad | |
1747 | .RS 12n | |
1748 | Set to attempt to recover from fatal errors. This should only be used as a | |
1749 | last resort, as it typically results in leaked space, or worse. | |
1750 | .sp | |
1751 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
1752 | .RE | |
1753 | ||
1754 | .sp | |
1755 | .ne 2 | |
1756 | .na | |
1757 | \fBzfs_resilver_min_time_ms\fR (int) | |
1758 | .ad | |
1759 | .RS 12n | |
1760 | Resilvers are processed by the sync thread. While resilvering it will spend | |
1761 | at least this much time working on a resilver between txg flushes. | |
1762 | .sp | |
1763 | Default value: \fB3,000\fR. | |
1764 | .RE | |
1765 | ||
1766 | .sp | |
1767 | .ne 2 | |
1768 | .na | |
1769 | \fBzfs_scan_ignore_errors\fR (int) | |
1770 | .ad | |
1771 | .RS 12n | |
1772 | If set to a nonzero value, remove the DTL (dirty time list) upon | |
1773 | completion of a pool scan (scrub) even if there were unrepairable | |
1774 | errors. It is intended to be used during pool repair or recovery to | |
1775 | stop resilvering when the pool is next imported. | |
1776 | .sp | |
1777 | Default value: \fB0\fR. | |
1778 | .RE | |
1779 | ||
1780 | .sp | |
1781 | .ne 2 | |
1782 | .na | |
1783 | \fBzfs_scrub_min_time_ms\fR (int) | |
1784 | .ad | |
1785 | .RS 12n | |
1786 | Scrubs are processed by the sync thread. While scrubbing it will spend | |
1787 | at least this much time working on a scrub between txg flushes. | |
1788 | .sp | |
1789 | Default value: \fB1,000\fR. | |
1790 | .RE | |
1791 | ||
1792 | .sp | |
1793 | .ne 2 | |
1794 | .na | |
1795 | \fBzfs_scan_checkpoint_intval\fR (int) | |
1796 | .ad | |
1797 | .RS 12n | |
1798 | To preserve progress across reboots the sequential scan algorithm periodically | |
1799 | needs to stop metadata scanning and issue all the verifications I/Os to disk. | |
1800 | The frequency of this flushing is determined by the | |
1801 | \fBfBzfs_scan_checkpoint_intval\fR tunable. | |
1802 | .sp | |
1803 | Default value: \fB7200\fR seconds (every 2 hours). | |
1804 | .RE | |
1805 | ||
1806 | .sp | |
1807 | .ne 2 | |
1808 | .na | |
1809 | \fBzfs_scan_fill_weight\fR (int) | |
1810 | .ad | |
1811 | .RS 12n | |
1812 | This tunable affects how scrub and resilver I/O segments are ordered. A higher | |
1813 | number indicates that we care more about how filled in a segment is, while a | |
1814 | lower number indicates we care more about the size of the extent without | |
1815 | considering the gaps within a segment. This value is only tunable upon module | |
1816 | insertion. Changing the value afterwards will have no affect on scrub or | |
1817 | resilver performance. | |
1818 | .sp | |
1819 | Default value: \fB3\fR. | |
1820 | .RE | |
1821 | ||
1822 | .sp | |
1823 | .ne 2 | |
1824 | .na | |
1825 | \fBzfs_scan_issue_strategy\fR (int) | |
1826 | .ad | |
1827 | .RS 12n | |
1828 | Determines the order that data will be verified while scrubbing or resilvering. | |
1829 | If set to \fB1\fR, data will be verified as sequentially as possible, given the | |
1830 | amount of memory reserved for scrubbing (see \fBzfs_scan_mem_lim_fact\fR). This | |
1831 | may improve scrub performance if the pool's data is very fragmented. If set to | |
1832 | \fB2\fR, the largest mostly-contiguous chunk of found data will be verified | |
1833 | first. By deferring scrubbing of small segments, we may later find adjacent data | |
1834 | to coalesce and increase the segment size. If set to \fB0\fR, zfs will use | |
1835 | strategy \fB1\fR during normal verification and strategy \fB2\fR while taking a | |
1836 | checkpoint. | |
1837 | .sp | |
1838 | Default value: \fB0\fR. | |
1839 | .RE | |
1840 | ||
1841 | .sp | |
1842 | .ne 2 | |
1843 | .na | |
1844 | \fBzfs_scan_legacy\fR (int) | |
1845 | .ad | |
1846 | .RS 12n | |
1847 | A value of 0 indicates that scrubs and resilvers will gather metadata in | |
1848 | memory before issuing sequential I/O. A value of 1 indicates that the legacy | |
1849 | algorithm will be used where I/O is initiated as soon as it is discovered. | |
1850 | Changing this value to 0 will not affect scrubs or resilvers that are already | |
1851 | in progress. | |
1852 | .sp | |
1853 | Default value: \fB0\fR. | |
1854 | .RE | |
1855 | ||
1856 | .sp | |
1857 | .ne 2 | |
1858 | .na | |
1859 | \fBzfs_scan_max_ext_gap\fR (int) | |
1860 | .ad | |
1861 | .RS 12n | |
1862 | Indicates the largest gap in bytes between scrub / resilver I/Os that will still | |
1863 | be considered sequential for sorting purposes. Changing this value will not | |
1864 | affect scrubs or resilvers that are already in progress. | |
1865 | .sp | |
1866 | Default value: \fB2097152 (2 MB)\fR. | |
1867 | .RE | |
1868 | ||
1869 | .sp | |
1870 | .ne 2 | |
1871 | .na | |
1872 | \fBzfs_scan_mem_lim_fact\fR (int) | |
1873 | .ad | |
1874 | .RS 12n | |
1875 | Maximum fraction of RAM used for I/O sorting by sequential scan algorithm. | |
1876 | This tunable determines the hard limit for I/O sorting memory usage. | |
1877 | When the hard limit is reached we stop scanning metadata and start issuing | |
1878 | data verification I/O. This is done until we get below the soft limit. | |
1879 | .sp | |
1880 | Default value: \fB20\fR which is 5% of RAM (1/20). | |
1881 | .RE | |
1882 | ||
1883 | .sp | |
1884 | .ne 2 | |
1885 | .na | |
1886 | \fBzfs_scan_mem_lim_soft_fact\fR (int) | |
1887 | .ad | |
1888 | .RS 12n | |
1889 | The fraction of the hard limit used to determined the soft limit for I/O sorting | |
1890 | by the sequential scan algorithm. When we cross this limit from bellow no action | |
1891 | is taken. When we cross this limit from above it is because we are issuing | |
1892 | verification I/O. In this case (unless the metadata scan is done) we stop | |
1893 | issuing verification I/O and start scanning metadata again until we get to the | |
1894 | hard limit. | |
1895 | .sp | |
1896 | Default value: \fB20\fR which is 5% of the hard limit (1/20). | |
1897 | .RE | |
1898 | ||
1899 | .sp | |
1900 | .ne 2 | |
1901 | .na | |
1902 | \fBzfs_scan_vdev_limit\fR (int) | |
1903 | .ad | |
1904 | .RS 12n | |
1905 | Maximum amount of data that can be concurrently issued at once for scrubs and | |
1906 | resilvers per leaf device, given in bytes. | |
1907 | .sp | |
1908 | Default value: \fB41943040\fR. | |
1909 | .RE | |
1910 | ||
1911 | .sp | |
1912 | .ne 2 | |
1913 | .na | |
1914 | \fBzfs_send_corrupt_data\fR (int) | |
1915 | .ad | |
1916 | .RS 12n | |
1917 | Allow sending of corrupt data (ignore read/checksum errors when sending data) | |
1918 | .sp | |
1919 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
1920 | .RE | |
1921 | ||
1922 | .sp | |
1923 | .ne 2 | |
1924 | .na | |
1925 | \fBzfs_sync_pass_deferred_free\fR (int) | |
1926 | .ad | |
1927 | .RS 12n | |
1928 | Flushing of data to disk is done in passes. Defer frees starting in this pass | |
1929 | .sp | |
1930 | Default value: \fB2\fR. | |
1931 | .RE | |
1932 | ||
1933 | .sp | |
1934 | .ne 2 | |
1935 | .na | |
1936 | \fBzfs_sync_pass_dont_compress\fR (int) | |
1937 | .ad | |
1938 | .RS 12n | |
1939 | Don't compress starting in this pass | |
1940 | .sp | |
1941 | Default value: \fB5\fR. | |
1942 | .RE | |
1943 | ||
1944 | .sp | |
1945 | .ne 2 | |
1946 | .na | |
1947 | \fBzfs_sync_pass_rewrite\fR (int) | |
1948 | .ad | |
1949 | .RS 12n | |
1950 | Rewrite new block pointers starting in this pass | |
1951 | .sp | |
1952 | Default value: \fB2\fR. | |
1953 | .RE | |
1954 | ||
1955 | .sp | |
1956 | .ne 2 | |
1957 | .na | |
1958 | \fBzfs_sync_taskq_batch_pct\fR (int) | |
1959 | .ad | |
1960 | .RS 12n | |
1961 | This controls the number of threads used by the dp_sync_taskq. The default | |
1962 | value of 75% will create a maximum of one thread per cpu. | |
1963 | .sp | |
1964 | Default value: \fB75\fR%. | |
1965 | .RE | |
1966 | ||
1967 | .sp | |
1968 | .ne 2 | |
1969 | .na | |
1970 | \fBzfs_txg_history\fR (int) | |
1971 | .ad | |
1972 | .RS 12n | |
1973 | Historical statistics for the last N txgs will be available in | |
1974 | \fB/proc/spl/kstat/zfs/<pool>/txgs\fR | |
1975 | .sp | |
1976 | Default value: \fB0\fR. | |
1977 | .RE | |
1978 | ||
1979 | .sp | |
1980 | .ne 2 | |
1981 | .na | |
1982 | \fBzfs_txg_timeout\fR (int) | |
1983 | .ad | |
1984 | .RS 12n | |
1985 | Flush dirty data to disk at least every N seconds (maximum txg duration) | |
1986 | .sp | |
1987 | Default value: \fB5\fR. | |
1988 | .RE | |
1989 | ||
1990 | .sp | |
1991 | .ne 2 | |
1992 | .na | |
1993 | \fBzfs_vdev_aggregation_limit\fR (int) | |
1994 | .ad | |
1995 | .RS 12n | |
1996 | Max vdev I/O aggregation size | |
1997 | .sp | |
1998 | Default value: \fB131,072\fR. | |
1999 | .RE | |
2000 | ||
2001 | .sp | |
2002 | .ne 2 | |
2003 | .na | |
2004 | \fBzfs_vdev_cache_bshift\fR (int) | |
2005 | .ad | |
2006 | .RS 12n | |
2007 | Shift size to inflate reads too | |
2008 | .sp | |
2009 | Default value: \fB16\fR (effectively 65536). | |
2010 | .RE | |
2011 | ||
2012 | .sp | |
2013 | .ne 2 | |
2014 | .na | |
2015 | \fBzfs_vdev_cache_max\fR (int) | |
2016 | .ad | |
2017 | .RS 12n | |
2018 | Inflate reads smaller than this value to meet the \fBzfs_vdev_cache_bshift\fR | |
2019 | size (default 64k). | |
2020 | .sp | |
2021 | Default value: \fB16384\fR. | |
2022 | .RE | |
2023 | ||
2024 | .sp | |
2025 | .ne 2 | |
2026 | .na | |
2027 | \fBzfs_vdev_cache_size\fR (int) | |
2028 | .ad | |
2029 | .RS 12n | |
2030 | Total size of the per-disk cache in bytes. | |
2031 | .sp | |
2032 | Currently this feature is disabled as it has been found to not be helpful | |
2033 | for performance and in some cases harmful. | |
2034 | .sp | |
2035 | Default value: \fB0\fR. | |
2036 | .RE | |
2037 | ||
2038 | .sp | |
2039 | .ne 2 | |
2040 | .na | |
2041 | \fBzfs_vdev_mirror_rotating_inc\fR (int) | |
2042 | .ad | |
2043 | .RS 12n | |
2044 | A number by which the balancing algorithm increments the load calculation for | |
2045 | the purpose of selecting the least busy mirror member when an I/O immediately | |
2046 | follows its predecessor on rotational vdevs for the purpose of making decisions | |
2047 | based on load. | |
2048 | .sp | |
2049 | Default value: \fB0\fR. | |
2050 | .RE | |
2051 | ||
2052 | .sp | |
2053 | .ne 2 | |
2054 | .na | |
2055 | \fBzfs_vdev_mirror_rotating_seek_inc\fR (int) | |
2056 | .ad | |
2057 | .RS 12n | |
2058 | A number by which the balancing algorithm increments the load calculation for | |
2059 | the purpose of selecting the least busy mirror member when an I/O lacks | |
2060 | locality as defined by the zfs_vdev_mirror_rotating_seek_offset. I/Os within | |
2061 | this that are not immediately following the previous I/O are incremented by | |
2062 | half. | |
2063 | .sp | |
2064 | Default value: \fB5\fR. | |
2065 | .RE | |
2066 | ||
2067 | .sp | |
2068 | .ne 2 | |
2069 | .na | |
2070 | \fBzfs_vdev_mirror_rotating_seek_offset\fR (int) | |
2071 | .ad | |
2072 | .RS 12n | |
2073 | The maximum distance for the last queued I/O in which the balancing algorithm | |
2074 | considers an I/O to have locality. | |
2075 | See the section "ZFS I/O SCHEDULER". | |
2076 | .sp | |
2077 | Default value: \fB1048576\fR. | |
2078 | .RE | |
2079 | ||
2080 | .sp | |
2081 | .ne 2 | |
2082 | .na | |
2083 | \fBzfs_vdev_mirror_non_rotating_inc\fR (int) | |
2084 | .ad | |
2085 | .RS 12n | |
2086 | A number by which the balancing algorithm increments the load calculation for | |
2087 | the purpose of selecting the least busy mirror member on non-rotational vdevs | |
2088 | when I/Os do not immediately follow one another. | |
2089 | .sp | |
2090 | Default value: \fB0\fR. | |
2091 | .RE | |
2092 | ||
2093 | .sp | |
2094 | .ne 2 | |
2095 | .na | |
2096 | \fBzfs_vdev_mirror_non_rotating_seek_inc\fR (int) | |
2097 | .ad | |
2098 | .RS 12n | |
2099 | A number by which the balancing algorithm increments the load calculation for | |
2100 | the purpose of selecting the least busy mirror member when an I/O lacks | |
2101 | locality as defined by the zfs_vdev_mirror_rotating_seek_offset. I/Os within | |
2102 | this that are not immediately following the previous I/O are incremented by | |
2103 | half. | |
2104 | .sp | |
2105 | Default value: \fB1\fR. | |
2106 | .RE | |
2107 | ||
2108 | .sp | |
2109 | .ne 2 | |
2110 | .na | |
2111 | \fBzfs_vdev_read_gap_limit\fR (int) | |
2112 | .ad | |
2113 | .RS 12n | |
2114 | Aggregate read I/O operations if the gap on-disk between them is within this | |
2115 | threshold. | |
2116 | .sp | |
2117 | Default value: \fB32,768\fR. | |
2118 | .RE | |
2119 | ||
2120 | .sp | |
2121 | .ne 2 | |
2122 | .na | |
2123 | \fBzfs_vdev_scheduler\fR (charp) | |
2124 | .ad | |
2125 | .RS 12n | |
2126 | Set the Linux I/O scheduler on whole disk vdevs to this scheduler. Valid options | |
2127 | are noop, cfq, bfq & deadline | |
2128 | .sp | |
2129 | Default value: \fBnoop\fR. | |
2130 | .RE | |
2131 | ||
2132 | .sp | |
2133 | .ne 2 | |
2134 | .na | |
2135 | \fBzfs_vdev_write_gap_limit\fR (int) | |
2136 | .ad | |
2137 | .RS 12n | |
2138 | Aggregate write I/O over gap | |
2139 | .sp | |
2140 | Default value: \fB4,096\fR. | |
2141 | .RE | |
2142 | ||
2143 | .sp | |
2144 | .ne 2 | |
2145 | .na | |
2146 | \fBzfs_vdev_raidz_impl\fR (string) | |
2147 | .ad | |
2148 | .RS 12n | |
2149 | Parameter for selecting raidz parity implementation to use. | |
2150 | ||
2151 | Options marked (always) below may be selected on module load as they are | |
2152 | supported on all systems. | |
2153 | The remaining options may only be set after the module is loaded, as they | |
2154 | are available only if the implementations are compiled in and supported | |
2155 | on the running system. | |
2156 | ||
2157 | Once the module is loaded, the content of | |
2158 | /sys/module/zfs/parameters/zfs_vdev_raidz_impl will show available options | |
2159 | with the currently selected one enclosed in []. | |
2160 | Possible options are: | |
2161 | fastest - (always) implementation selected using built-in benchmark | |
2162 | original - (always) original raidz implementation | |
2163 | scalar - (always) scalar raidz implementation | |
2164 | sse2 - implementation using SSE2 instruction set (64bit x86 only) | |
2165 | ssse3 - implementation using SSSE3 instruction set (64bit x86 only) | |
2166 | avx2 - implementation using AVX2 instruction set (64bit x86 only) | |
2167 | avx512f - implementation using AVX512F instruction set (64bit x86 only) | |
2168 | avx512bw - implementation using AVX512F & AVX512BW instruction sets (64bit x86 only) | |
2169 | aarch64_neon - implementation using NEON (Aarch64/64 bit ARMv8 only) | |
2170 | aarch64_neonx2 - implementation using NEON with more unrolling (Aarch64/64 bit ARMv8 only) | |
2171 | .sp | |
2172 | Default value: \fBfastest\fR. | |
2173 | .RE | |
2174 | ||
2175 | .sp | |
2176 | .ne 2 | |
2177 | .na | |
2178 | \fBzfs_zevent_cols\fR (int) | |
2179 | .ad | |
2180 | .RS 12n | |
2181 | When zevents are logged to the console use this as the word wrap width. | |
2182 | .sp | |
2183 | Default value: \fB80\fR. | |
2184 | .RE | |
2185 | ||
2186 | .sp | |
2187 | .ne 2 | |
2188 | .na | |
2189 | \fBzfs_zevent_console\fR (int) | |
2190 | .ad | |
2191 | .RS 12n | |
2192 | Log events to the console | |
2193 | .sp | |
2194 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
2195 | .RE | |
2196 | ||
2197 | .sp | |
2198 | .ne 2 | |
2199 | .na | |
2200 | \fBzfs_zevent_len_max\fR (int) | |
2201 | .ad | |
2202 | .RS 12n | |
2203 | Max event queue length. A value of 0 will result in a calculated value which | |
2204 | increases with the number of CPUs in the system (minimum 64 events). Events | |
2205 | in the queue can be viewed with the \fBzpool events\fR command. | |
2206 | .sp | |
2207 | Default value: \fB0\fR. | |
2208 | .RE | |
2209 | ||
2210 | .sp | |
2211 | .ne 2 | |
2212 | .na | |
2213 | \fBzfs_zil_clean_taskq_maxalloc\fR (int) | |
2214 | .ad | |
2215 | .RS 12n | |
2216 | The maximum number of taskq entries that are allowed to be cached. When this | |
2217 | limit is exceeded transaction records (itxs) will be cleaned synchronously. | |
2218 | .sp | |
2219 | Default value: \fB1048576\fR. | |
2220 | .RE | |
2221 | ||
2222 | .sp | |
2223 | .ne 2 | |
2224 | .na | |
2225 | \fBzfs_zil_clean_taskq_minalloc\fR (int) | |
2226 | .ad | |
2227 | .RS 12n | |
2228 | The number of taskq entries that are pre-populated when the taskq is first | |
2229 | created and are immediately available for use. | |
2230 | .sp | |
2231 | Default value: \fB1024\fR. | |
2232 | .RE | |
2233 | ||
2234 | .sp | |
2235 | .ne 2 | |
2236 | .na | |
2237 | \fBzfs_zil_clean_taskq_nthr_pct\fR (int) | |
2238 | .ad | |
2239 | .RS 12n | |
2240 | This controls the number of threads used by the dp_zil_clean_taskq. The default | |
2241 | value of 100% will create a maximum of one thread per cpu. | |
2242 | .sp | |
2243 | Default value: \fB100\fR%. | |
2244 | .RE | |
2245 | ||
2246 | .sp | |
2247 | .ne 2 | |
2248 | .na | |
2249 | \fBzil_replay_disable\fR (int) | |
2250 | .ad | |
2251 | .RS 12n | |
2252 | Disable intent logging replay. Can be disabled for recovery from corrupted | |
2253 | ZIL | |
2254 | .sp | |
2255 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
2256 | .RE | |
2257 | ||
2258 | .sp | |
2259 | .ne 2 | |
2260 | .na | |
2261 | \fBzil_slog_bulk\fR (ulong) | |
2262 | .ad | |
2263 | .RS 12n | |
2264 | Limit SLOG write size per commit executed with synchronous priority. | |
2265 | Any writes above that will be executed with lower (asynchronous) priority | |
2266 | to limit potential SLOG device abuse by single active ZIL writer. | |
2267 | .sp | |
2268 | Default value: \fB786,432\fR. | |
2269 | .RE | |
2270 | ||
2271 | .sp | |
2272 | .ne 2 | |
2273 | .na | |
2274 | \fBzio_delay_max\fR (int) | |
2275 | .ad | |
2276 | .RS 12n | |
2277 | A zevent will be logged if a ZIO operation takes more than N milliseconds to | |
2278 | complete. Note that this is only a logging facility, not a timeout on | |
2279 | operations. | |
2280 | .sp | |
2281 | Default value: \fB30,000\fR. | |
2282 | .RE | |
2283 | ||
2284 | .sp | |
2285 | .ne 2 | |
2286 | .na | |
2287 | \fBzio_dva_throttle_enabled\fR (int) | |
2288 | .ad | |
2289 | .RS 12n | |
2290 | Throttle block allocations in the ZIO pipeline. This allows for | |
2291 | dynamic allocation distribution when devices are imbalanced. | |
2292 | When enabled, the maximum number of pending allocations per top-level vdev | |
2293 | is limited by \fBzfs_vdev_queue_depth_pct\fR. | |
2294 | .sp | |
2295 | Default value: \fB1\fR. | |
2296 | .RE | |
2297 | ||
2298 | .sp | |
2299 | .ne 2 | |
2300 | .na | |
2301 | \fBzio_requeue_io_start_cut_in_line\fR (int) | |
2302 | .ad | |
2303 | .RS 12n | |
2304 | Prioritize requeued I/O | |
2305 | .sp | |
2306 | Default value: \fB0\fR. | |
2307 | .RE | |
2308 | ||
2309 | .sp | |
2310 | .ne 2 | |
2311 | .na | |
2312 | \fBzio_taskq_batch_pct\fR (uint) | |
2313 | .ad | |
2314 | .RS 12n | |
2315 | Percentage of online CPUs (or CPU cores, etc) which will run a worker thread | |
2316 | for IO. These workers are responsible for IO work such as compression and | |
2317 | checksum calculations. Fractional number of CPUs will be rounded down. | |
2318 | .sp | |
2319 | The default value of 75 was chosen to avoid using all CPUs which can result in | |
2320 | latency issues and inconsistent application performance, especially when high | |
2321 | compression is enabled. | |
2322 | .sp | |
2323 | Default value: \fB75\fR. | |
2324 | .RE | |
2325 | ||
2326 | .sp | |
2327 | .ne 2 | |
2328 | .na | |
2329 | \fBzvol_inhibit_dev\fR (uint) | |
2330 | .ad | |
2331 | .RS 12n | |
2332 | Do not create zvol device nodes. This may slightly improve startup time on | |
2333 | systems with a very large number of zvols. | |
2334 | .sp | |
2335 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
2336 | .RE | |
2337 | ||
2338 | .sp | |
2339 | .ne 2 | |
2340 | .na | |
2341 | \fBzvol_major\fR (uint) | |
2342 | .ad | |
2343 | .RS 12n | |
2344 | Major number for zvol block devices | |
2345 | .sp | |
2346 | Default value: \fB230\fR. | |
2347 | .RE | |
2348 | ||
2349 | .sp | |
2350 | .ne 2 | |
2351 | .na | |
2352 | \fBzvol_max_discard_blocks\fR (ulong) | |
2353 | .ad | |
2354 | .RS 12n | |
2355 | Discard (aka TRIM) operations done on zvols will be done in batches of this | |
2356 | many blocks, where block size is determined by the \fBvolblocksize\fR property | |
2357 | of a zvol. | |
2358 | .sp | |
2359 | Default value: \fB16,384\fR. | |
2360 | .RE | |
2361 | ||
2362 | .sp | |
2363 | .ne 2 | |
2364 | .na | |
2365 | \fBzvol_prefetch_bytes\fR (uint) | |
2366 | .ad | |
2367 | .RS 12n | |
2368 | When adding a zvol to the system prefetch \fBzvol_prefetch_bytes\fR | |
2369 | from the start and end of the volume. Prefetching these regions | |
2370 | of the volume is desirable because they are likely to be accessed | |
2371 | immediately by \fBblkid(8)\fR or by the kernel scanning for a partition | |
2372 | table. | |
2373 | .sp | |
2374 | Default value: \fB131,072\fR. | |
2375 | .RE | |
2376 | ||
2377 | .sp | |
2378 | .ne 2 | |
2379 | .na | |
2380 | \fBzvol_request_sync\fR (uint) | |
2381 | .ad | |
2382 | .RS 12n | |
2383 | When processing I/O requests for a zvol submit them synchronously. This | |
2384 | effectively limits the queue depth to 1 for each I/O submitter. When set | |
2385 | to 0 requests are handled asynchronously by a thread pool. The number of | |
2386 | requests which can be handled concurrently is controller by \fBzvol_threads\fR. | |
2387 | .sp | |
2388 | Default value: \fB0\fR. | |
2389 | .RE | |
2390 | ||
2391 | .sp | |
2392 | .ne 2 | |
2393 | .na | |
2394 | \fBzvol_threads\fR (uint) | |
2395 | .ad | |
2396 | .RS 12n | |
2397 | Max number of threads which can handle zvol I/O requests concurrently. | |
2398 | .sp | |
2399 | Default value: \fB32\fR. | |
2400 | .RE | |
2401 | ||
2402 | .sp | |
2403 | .ne 2 | |
2404 | .na | |
2405 | \fBzvol_volmode\fR (uint) | |
2406 | .ad | |
2407 | .RS 12n | |
2408 | Defines zvol block devices behaviour when \fBvolmode\fR is set to \fBdefault\fR. | |
2409 | Valid values are \fB1\fR (full), \fB2\fR (dev) and \fB3\fR (none). | |
2410 | .sp | |
2411 | Default value: \fB1\fR. | |
2412 | .RE | |
2413 | ||
2414 | .sp | |
2415 | .ne 2 | |
2416 | .na | |
2417 | \fBzfs_qat_disable\fR (int) | |
2418 | .ad | |
2419 | .RS 12n | |
2420 | This tunable disables qat hardware acceleration for gzip compression and. | |
2421 | AES-GCM encryption. It is available only if qat acceleration is compiled in | |
2422 | and the qat driver is present. | |
2423 | .sp | |
2424 | Use \fB1\fR for yes and \fB0\fR for no (default). | |
2425 | .RE | |
2426 | ||
2427 | .SH ZFS I/O SCHEDULER | |
2428 | ZFS issues I/O operations to leaf vdevs to satisfy and complete I/Os. | |
2429 | The I/O scheduler determines when and in what order those operations are | |
2430 | issued. The I/O scheduler divides operations into five I/O classes | |
2431 | prioritized in the following order: sync read, sync write, async read, | |
2432 | async write, and scrub/resilver. Each queue defines the minimum and | |
2433 | maximum number of concurrent operations that may be issued to the | |
2434 | device. In addition, the device has an aggregate maximum, | |
2435 | \fBzfs_vdev_max_active\fR. Note that the sum of the per-queue minimums | |
2436 | must not exceed the aggregate maximum. If the sum of the per-queue | |
2437 | maximums exceeds the aggregate maximum, then the number of active I/Os | |
2438 | may reach \fBzfs_vdev_max_active\fR, in which case no further I/Os will | |
2439 | be issued regardless of whether all per-queue minimums have been met. | |
2440 | .sp | |
2441 | For many physical devices, throughput increases with the number of | |
2442 | concurrent operations, but latency typically suffers. Further, physical | |
2443 | devices typically have a limit at which more concurrent operations have no | |
2444 | effect on throughput or can actually cause it to decrease. | |
2445 | .sp | |
2446 | The scheduler selects the next operation to issue by first looking for an | |
2447 | I/O class whose minimum has not been satisfied. Once all are satisfied and | |
2448 | the aggregate maximum has not been hit, the scheduler looks for classes | |
2449 | whose maximum has not been satisfied. Iteration through the I/O classes is | |
2450 | done in the order specified above. No further operations are issued if the | |
2451 | aggregate maximum number of concurrent operations has been hit or if there | |
2452 | are no operations queued for an I/O class that has not hit its maximum. | |
2453 | Every time an I/O is queued or an operation completes, the I/O scheduler | |
2454 | looks for new operations to issue. | |
2455 | .sp | |
2456 | In general, smaller max_active's will lead to lower latency of synchronous | |
2457 | operations. Larger max_active's may lead to higher overall throughput, | |
2458 | depending on underlying storage. | |
2459 | .sp | |
2460 | The ratio of the queues' max_actives determines the balance of performance | |
2461 | between reads, writes, and scrubs. E.g., increasing | |
2462 | \fBzfs_vdev_scrub_max_active\fR will cause the scrub or resilver to complete | |
2463 | more quickly, but reads and writes to have higher latency and lower throughput. | |
2464 | .sp | |
2465 | All I/O classes have a fixed maximum number of outstanding operations | |
2466 | except for the async write class. Asynchronous writes represent the data | |
2467 | that is committed to stable storage during the syncing stage for | |
2468 | transaction groups. Transaction groups enter the syncing state | |
2469 | periodically so the number of queued async writes will quickly burst up | |
2470 | and then bleed down to zero. Rather than servicing them as quickly as | |
2471 | possible, the I/O scheduler changes the maximum number of active async | |
2472 | write I/Os according to the amount of dirty data in the pool. Since | |
2473 | both throughput and latency typically increase with the number of | |
2474 | concurrent operations issued to physical devices, reducing the | |
2475 | burstiness in the number of concurrent operations also stabilizes the | |
2476 | response time of operations from other -- and in particular synchronous | |
2477 | -- queues. In broad strokes, the I/O scheduler will issue more | |
2478 | concurrent operations from the async write queue as there's more dirty | |
2479 | data in the pool. | |
2480 | .sp | |
2481 | Async Writes | |
2482 | .sp | |
2483 | The number of concurrent operations issued for the async write I/O class | |
2484 | follows a piece-wise linear function defined by a few adjustable points. | |
2485 | .nf | |
2486 | ||
2487 | | o---------| <-- zfs_vdev_async_write_max_active | |
2488 | ^ | /^ | | |
2489 | | | / | | | |
2490 | active | / | | | |
2491 | I/O | / | | | |
2492 | count | / | | | |
2493 | | / | | | |
2494 | |-------o | | <-- zfs_vdev_async_write_min_active | |
2495 | 0|_______^______|_________| | |
2496 | 0% | | 100% of zfs_dirty_data_max | |
2497 | | | | |
2498 | | `-- zfs_vdev_async_write_active_max_dirty_percent | |
2499 | `--------- zfs_vdev_async_write_active_min_dirty_percent | |
2500 | ||
2501 | .fi | |
2502 | Until the amount of dirty data exceeds a minimum percentage of the dirty | |
2503 | data allowed in the pool, the I/O scheduler will limit the number of | |
2504 | concurrent operations to the minimum. As that threshold is crossed, the | |
2505 | number of concurrent operations issued increases linearly to the maximum at | |
2506 | the specified maximum percentage of the dirty data allowed in the pool. | |
2507 | .sp | |
2508 | Ideally, the amount of dirty data on a busy pool will stay in the sloped | |
2509 | part of the function between \fBzfs_vdev_async_write_active_min_dirty_percent\fR | |
2510 | and \fBzfs_vdev_async_write_active_max_dirty_percent\fR. If it exceeds the | |
2511 | maximum percentage, this indicates that the rate of incoming data is | |
2512 | greater than the rate that the backend storage can handle. In this case, we | |
2513 | must further throttle incoming writes, as described in the next section. | |
2514 | ||
2515 | .SH ZFS TRANSACTION DELAY | |
2516 | We delay transactions when we've determined that the backend storage | |
2517 | isn't able to accommodate the rate of incoming writes. | |
2518 | .sp | |
2519 | If there is already a transaction waiting, we delay relative to when | |
2520 | that transaction will finish waiting. This way the calculated delay time | |
2521 | is independent of the number of threads concurrently executing | |
2522 | transactions. | |
2523 | .sp | |
2524 | If we are the only waiter, wait relative to when the transaction | |
2525 | started, rather than the current time. This credits the transaction for | |
2526 | "time already served", e.g. reading indirect blocks. | |
2527 | .sp | |
2528 | The minimum time for a transaction to take is calculated as: | |
2529 | .nf | |
2530 | min_time = zfs_delay_scale * (dirty - min) / (max - dirty) | |
2531 | min_time is then capped at 100 milliseconds. | |
2532 | .fi | |
2533 | .sp | |
2534 | The delay has two degrees of freedom that can be adjusted via tunables. The | |
2535 | percentage of dirty data at which we start to delay is defined by | |
2536 | \fBzfs_delay_min_dirty_percent\fR. This should typically be at or above | |
2537 | \fBzfs_vdev_async_write_active_max_dirty_percent\fR so that we only start to | |
2538 | delay after writing at full speed has failed to keep up with the incoming write | |
2539 | rate. The scale of the curve is defined by \fBzfs_delay_scale\fR. Roughly speaking, | |
2540 | this variable determines the amount of delay at the midpoint of the curve. | |
2541 | .sp | |
2542 | .nf | |
2543 | delay | |
2544 | 10ms +-------------------------------------------------------------*+ | |
2545 | | *| | |
2546 | 9ms + *+ | |
2547 | | *| | |
2548 | 8ms + *+ | |
2549 | | * | | |
2550 | 7ms + * + | |
2551 | | * | | |
2552 | 6ms + * + | |
2553 | | * | | |
2554 | 5ms + * + | |
2555 | | * | | |
2556 | 4ms + * + | |
2557 | | * | | |
2558 | 3ms + * + | |
2559 | | * | | |
2560 | 2ms + (midpoint) * + | |
2561 | | | ** | | |
2562 | 1ms + v *** + | |
2563 | | zfs_delay_scale ----------> ******** | | |
2564 | 0 +-------------------------------------*********----------------+ | |
2565 | 0% <- zfs_dirty_data_max -> 100% | |
2566 | .fi | |
2567 | .sp | |
2568 | Note that since the delay is added to the outstanding time remaining on the | |
2569 | most recent transaction, the delay is effectively the inverse of IOPS. | |
2570 | Here the midpoint of 500us translates to 2000 IOPS. The shape of the curve | |
2571 | was chosen such that small changes in the amount of accumulated dirty data | |
2572 | in the first 3/4 of the curve yield relatively small differences in the | |
2573 | amount of delay. | |
2574 | .sp | |
2575 | The effects can be easier to understand when the amount of delay is | |
2576 | represented on a log scale: | |
2577 | .sp | |
2578 | .nf | |
2579 | delay | |
2580 | 100ms +-------------------------------------------------------------++ | |
2581 | + + | |
2582 | | | | |
2583 | + *+ | |
2584 | 10ms + *+ | |
2585 | + ** + | |
2586 | | (midpoint) ** | | |
2587 | + | ** + | |
2588 | 1ms + v **** + | |
2589 | + zfs_delay_scale ----------> ***** + | |
2590 | | **** | | |
2591 | + **** + | |
2592 | 100us + ** + | |
2593 | + * + | |
2594 | | * | | |
2595 | + * + | |
2596 | 10us + * + | |
2597 | + + | |
2598 | | | | |
2599 | + + | |
2600 | +--------------------------------------------------------------+ | |
2601 | 0% <- zfs_dirty_data_max -> 100% | |
2602 | .fi | |
2603 | .sp | |
2604 | Note here that only as the amount of dirty data approaches its limit does | |
2605 | the delay start to increase rapidly. The goal of a properly tuned system | |
2606 | should be to keep the amount of dirty data out of that range by first | |
2607 | ensuring that the appropriate limits are set for the I/O scheduler to reach | |
2608 | optimal throughput on the backend storage, and then by changing the value | |
2609 | of \fBzfs_delay_scale\fR to increase the steepness of the curve. |