Default value: \fB6\fR.
.RE
+.sp
+.ne 2
+.na
+\fBdmu_prefetch_max\fR (int)
+.ad
+.RS 12n
+Limit the amount we can prefetch with one call to this amount (in bytes).
+This helps to limit the amount of memory that can be used by prefetching.
+.sp
+Default value: \fB134,217,728\fR (128MB).
+.RE
+
.sp
.ne 2
.na
Use \fB1\fR for yes (default) and \fB0\fR for no.
.RE
+.sp
+.ne 2
+.na
+\fBmetaslab_df_max_search\fR (int)
+.ad
+.RS 12n
+Maximum distance to search forward from the last offset. Without this limit,
+fragmented pools can see >100,000 iterations and metaslab_block_picker()
+becomes the performance limiting factor on high-performance storage.
+
+With the default setting of 16MB, we typically see less than 500 iterations,
+even with very fragmented, ashift=9 pools. The maximum number of iterations
+possible is: \fBmetaslab_df_max_search / (2 * (1<<ashift))\fR.
+With the default setting of 16MB this is 16*1024 (with ashift=9) or 2048
+(with ashift=12).
+.sp
+Default value: \fB16,777,216\fR (16MB)
+.RE
+
+.sp
+.ne 2
+.na
+\fBmetaslab_df_use_largest_segment\fR (int)
+.ad
+.RS 12n
+If we are not searching forward (due to metaslab_df_max_search,
+metaslab_df_free_pct, or metaslab_df_alloc_threshold), this tunable controls
+what segment is used. If it is set, we will use the largest free segment.
+If it is not set, we will use a segment of exactly the requested size (or
+larger).
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
.sp
.ne 2
.na
.ad
.RS 12n
When set, the hole_birth optimization will not be used, and all holes will
-always be sent on zfs send. Useful if you suspect your datasets are affected
-by a bug in hole_birth.
+always be sent on zfs send. This is useful if you suspect your datasets are
+affected by a bug in hole_birth.
.sp
Use \fB1\fR for on (default) and \fB0\fR for off.
.RE
Default value: \fB32,768\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzap_iterate_prefetch\fR (int)
+.ad
+.RS 12n
+If this is set, when we start iterating over a ZAP object, zfs will prefetch
+the entire object (all leaf blocks). However, this is limited by
+\fBdmu_prefetch_max\fR.
+.sp
+Use \fB1\fR for on (default) and \fB0\fR for off.
+.RE
+
.sp
.ne 2
.na
Default value: \fB1,048,576\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_allow_redacted_dataset_mount\fR (int)
+.ad
+.RS 12n
+Allow datasets received with redacted send/receive to be mounted. Normally
+disabled because these datasets may be missing key data.
+.sp
+Default value: \fB0\fR.
+.RE
+
.sp
.ne 2
.na
skipped unless all metaslab groups within the metaslab class have also
crossed this threshold.
.sp
-Default value: \fB85\fR.
+Default value: \fB95\fR.
.RE
.sp
Default value: \fB0\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_removal_suspend_progress\fR (int)
+.ad
+.RS 12n
+.sp
+This is used by the test suite so that it can ensure that certain actions
+happen while in the middle of a removal.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_remove_max_segment\fR (int)
+.ad
+.RS 12n
+.sp
+The largest contiguous segment that we will attempt to allocate when removing
+a device. This can be no larger than 16MB. If there is a performance
+problem with attempting to allocate large blocks, consider decreasing this.
+.sp
+Default value: \fB16,777,216\fR (16MB).
+.RE
+
.sp
.ne 2
.na
Use \fB1\fR for yes and \fB0\fR for no (default).
.RE
+.sp
+.ne 2
+.na
+\fBzfs_send_unmodified_spill_blocks\fR (int)
+.ad
+.RS 12n
+Include unmodified spill blocks in the send stream. Under certain circumstances
+previous versions of ZFS could incorrectly remove the spill block from an
+existing object. Including unmodified copies of the spill blocks creates a
+backwards compatible stream which will recreate a spill block if it was
+incorrectly removed.
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR for no.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_send_no_prefetch_queue_ff\fR (int)
+.ad
+.RS 12n
+The fill fraction of the \fBzfs send\fR internal queues. The fill fraction
+controls the timing with which internal threads are woken up.
+.sp
+Default value: \fB20\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_send_no_prefetch_queue_length\fR (int)
+.ad
+.RS 12n
+The maximum number of bytes allowed in \fBzfs send\fR's internal queues.
+.sp
+Default value: \fB1,048,576\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_send_queue_ff\fR (int)
+.ad
+.RS 12n
+The fill fraction of the \fBzfs send\fR prefetch queue. The fill fraction
+controls the timing with which internal threads are woken up.
+.sp
+Default value: \fB20\fR.
+.RE
+
.sp
.ne 2
.na
\fBzfs_send_queue_length\fR (int)
.ad
.RS 12n
-The maximum number of bytes allowed in the \fBzfs send\fR queue. This value
-must be at least twice the maximum block size in use.
+The maximum number of bytes allowed that will be prefetched by \fBzfs send\fR.
+This value must be at least twice the maximum block size in use.
.sp
Default value: \fB16,777,216\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_recv_queue_length\fR (int)
+\fBzfs_recv_queue_ff\fR (int)
.ad
.RS 12n
+The fill fraction of the \fBzfs receive\fR queue. The fill fraction
+controls the timing with which internal threads are woken up.
+.sp
+Default value: \fB20\fR.
+.RE
+
.sp
+.ne 2
+.na
+\fBzfs_recv_queue_length\fR (int)
+.ad
+.RS 12n
The maximum number of bytes allowed in the \fBzfs receive\fR queue. This value
must be at least twice the maximum block size in use.
.sp
Default value: \fB16,777,216\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_override_estimate_recordsize\fR (ulong)
+.ad
+.RS 12n
+Setting this variable overrides the default logic for estimating block
+sizes when doing a zfs send. The default heuristic is that the average
+block size will be the current recordsize. Override this value if most data
+in your dataset is not of that size and you require accurate zfs send size
+estimates.
+.sp
+Default value: \fB0\fR.
+.RE
+
.sp
.ne 2
.na
Default value: \fB16,777,216\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_special_class_metadata_reserve_pct\fR (int)
+.ad
+.RS 12n
+Only allow small data blocks to be allocated on the special and dedup vdev
+types when the available free space percentage on these vdevs exceeds this
+value. This ensures reserved space is available for pool meta data as the
+special vdevs approach capacity.
+.sp
+Default value: \fB25\fR.
+.RE
+
.sp
.ne 2
.na
\fBzfs_sync_pass_dont_compress\fR (int)
.ad
.RS 12n
-Don't compress starting in this pass
+Starting in this sync pass, we disable compression (including of metadata).
+With the default setting, in practice, we don't have this many sync passes,
+so this has no effect.
.sp
-Default value: \fB5\fR.
+The original intent was that disabling compression would help the sync passes
+to converge. However, in practice disabling compression increases the average
+number of sync passes, because when we turn compression off, a lot of block's
+size will change and thus we have to re-allocate (not overwrite) them. It
+also increases the number of 128KB allocations (e.g. for indirect blocks and
+spacemaps) because these will not be compressed. The 128K allocations are
+especially detrimental to performance on highly fragmented systems, which may
+have very few free segments of this size, and may need to load new metaslabs
+to satisfy 128K allocations.
+.sp
+Default value: \fB8\fR.
.RE
.sp
Default value: \fB100\fR%.
.RE
+.sp
+.ne 2
+.na
+\fBzil_maxblocksize\fR (int)
+.ad
+.RS 12n
+This sets the maximum block size used by the ZIL. On very fragmented pools,
+lowering this (typically to 36KB) can improve performance.
+.sp
+Default value: \fB131072\fR (128KB).
+.RE
+
.sp
.ne 2
.na
projects / mirror_zfs.git / blobdiff