'\" te
.\" Copyright (c) 2013 by Turbo Fredriksson <turbo@bayour.com>. All rights reserved.
+.\" Copyright (c) 2019 by Delphix. All rights reserved.
+.\" Copyright (c) 2019 Datto Inc.
.\" The contents of this file are subject to the terms of the Common Development
.\" and Distribution License (the "License"). You may not use this file except
.\" in compliance with the License. You can obtain a copy of the license at
.\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your
.\" own identifying information:
.\" Portions Copyright [yyyy] [name of copyright owner]
-.TH ZFS-MODULE-PARAMETERS 5 "Nov 16, 2013"
+.TH ZFS-MODULE-PARAMETERS 5 "Feb 15, 2019"
.SH NAME
zfs\-module\-parameters \- ZFS module parameters
.SH DESCRIPTION
.sp
.ne 2
.na
-\fBl2arc_feed_again\fR (int)
+\fBdbuf_cache_max_bytes\fR (ulong)
.ad
.RS 12n
-Turbo L2ARC warmup
+Maximum size in bytes of the dbuf cache. When \fB0\fR this value will default
+to \fB1/2^dbuf_cache_shift\fR (1/32) of the target ARC size, otherwise the
+provided value in bytes will be used. The behavior of the dbuf cache and its
+associated settings can be observed via the \fB/proc/spl/kstat/zfs/dbufstats\fR
+kstat.
.sp
-Use \fB1\fR for yes (default) and \fB0\fR to disable.
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBl2arc_feed_min_ms\fR (ulong)
+\fBdbuf_metadata_cache_max_bytes\fR (ulong)
.ad
.RS 12n
-Min feed interval in milliseconds
+Maximum size in bytes of the metadata dbuf cache. When \fB0\fR this value will
+default to \fB1/2^dbuf_cache_shift\fR (1/16) of the target ARC size, otherwise
+the provided value in bytes will be used. The behavior of the metadata dbuf
+cache and its associated settings can be observed via the
+\fB/proc/spl/kstat/zfs/dbufstats\fR kstat.
.sp
-Default value: \fB200\fR.
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBl2arc_feed_secs\fR (ulong)
+\fBdbuf_cache_hiwater_pct\fR (uint)
.ad
.RS 12n
-Seconds between L2ARC writing
+The percentage over \fBdbuf_cache_max_bytes\fR when dbufs must be evicted
+directly.
.sp
-Default value: \fB1\fR.
+Default value: \fB10\fR%.
.RE
.sp
.ne 2
.na
-\fBl2arc_headroom\fR (ulong)
+\fBdbuf_cache_lowater_pct\fR (uint)
.ad
.RS 12n
-Number of max device writes to precache
+The percentage below \fBdbuf_cache_max_bytes\fR when the evict thread stops
+evicting dbufs.
.sp
-Default value: \fB2\fR.
+Default value: \fB10\fR%.
.RE
.sp
.ne 2
.na
-\fBl2arc_headroom_boost\fR (ulong)
+\fBdbuf_cache_shift\fR (int)
+.ad
+.RS 12n
+Set the size of the dbuf cache, \fBdbuf_cache_max_bytes\fR, to a log2 fraction
+of the target arc size.
+.sp
+Default value: \fB5\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBdbuf_metadata_cache_shift\fR (int)
+.ad
+.RS 12n
+Set the size of the dbuf metadata cache, \fBdbuf_metadata_cache_max_bytes\fR,
+to a log2 fraction of the target arc size.
+.sp
+Default value: \fB6\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBignore_hole_birth\fR (int)
+.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.
+.sp
+Use \fB1\fR for on (default) and \fB0\fR for off.
+.RE
+
+.sp
+.ne 2
+.na
+\fBl2arc_feed_again\fR (int)
+.ad
+.RS 12n
+Turbo L2ARC warm-up. When the L2ARC is cold the fill interval will be set as
+fast as possible.
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR to disable.
+.RE
+
+.sp
+.ne 2
+.na
+\fBl2arc_feed_min_ms\fR (ulong)
.ad
.RS 12n
-Compressed l2arc_headroom multiplier
+Min feed interval in milliseconds. Requires \fBl2arc_feed_again=1\fR and only
+applicable in related situations.
.sp
Default value: \fB200\fR.
.RE
.sp
.ne 2
.na
-\fBl2arc_max_block_size\fR (ulong)
+\fBl2arc_feed_secs\fR (ulong)
.ad
.RS 12n
-The maximum block size which may be written to an L2ARC device, after
-compression and other factors. This setting is used to prevent a small
-number of large blocks from pushing a larger number of small blocks out
-of the cache.
+Seconds between L2ARC writing
.sp
-Default value: \fB16,777,216\fR.
+Default value: \fB1\fR.
.RE
.sp
.ne 2
.na
-\fBl2arc_nocompress\fR (int)
+\fBl2arc_headroom\fR (ulong)
.ad
.RS 12n
-Skip compressing L2ARC buffers
+How far through the ARC lists to search for L2ARC cacheable content, expressed
+as a multiplier of \fBl2arc_write_max\fR
.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
+Default value: \fB2\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBl2arc_headroom_boost\fR (ulong)
+.ad
+.RS 12n
+Scales \fBl2arc_headroom\fR by this percentage when L2ARC contents are being
+successfully compressed before writing. A value of 100 disables this feature.
+.sp
+Default value: \fB200\fR%.
.RE
.sp
\fBl2arc_noprefetch\fR (int)
.ad
.RS 12n
-Skip caching prefetched buffers
+Do not write buffers to L2ARC if they were prefetched but not used by
+applications
.sp
Use \fB1\fR for yes (default) and \fB0\fR to disable.
.RE
\fBl2arc_write_boost\fR (ulong)
.ad
.RS 12n
-Extra write bytes during device warmup
+Cold L2ARC devices will have \fBl2arc_write_max\fR increased by this amount
+while they remain cold.
.sp
Default value: \fB8,388,608\fR.
.RE
Use \fB1\fR for yes (default) and \fB0\fR for no.
.RE
+.sp
+.ne 2
+.na
+\fBmetaslab_force_ganging\fR (ulong)
+.ad
+.RS 12n
+Make some blocks above a certain size be gang blocks. This option is used
+by the test suite to facilitate testing.
+.sp
+Default value: \fB16,777,217\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_metaslab_segment_weight_enabled\fR (int)
+.ad
+.RS 12n
+Enable/disable segment-based metaslab selection.
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR for no.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_metaslab_switch_threshold\fR (int)
+.ad
+.RS 12n
+When using segment-based metaslab selection, continue allocating
+from the active metaslab until \fBzfs_metaslab_switch_threshold\fR
+worth of buckets have been exhausted.
+.sp
+Default value: \fB2\fR.
+.RE
+
.sp
.ne 2
.na
.sp
.ne 2
.na
-\fBmetaslabs_per_vdev\fR (int)
+\fBzfs_vdev_default_ms_count\fR (int)
.ad
.RS 12n
-When a vdev is added, it will be divided into approximately (but no more than) this number of metaslabs.
+When a vdev is added target this number of metaslabs per top-level vdev.
.sp
Default value: \fB200\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_vdev_min_ms_count\fR (int)
+.ad
+.RS 12n
+Minimum number of metaslabs to create in a top-level vdev.
+.sp
+Default value: \fB16\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBvdev_ms_count_limit\fR (int)
+.ad
+.RS 12n
+Practical upper limit of total metaslabs per top-level vdev.
+.sp
+Default value: \fB131,072\fR.
+.RE
+
.sp
.ne 2
.na
may wish to specify a more realistic inflation factor, particularly if
they operate close to quota or capacity limits.
.sp
-Default value: 24
+Default value: \fB24\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBspa_load_print_vdev_tree\fR (int)
+.ad
+.RS 12n
+Whether to print the vdev tree in the debugging message buffer during pool import.
+Use 0 to disable and 1 to enable.
+.sp
+Default value: \fB0\fR.
.RE
.sp
the traversal skips non-metadata blocks. It can be toggled once the
import has started to stop or start the traversal of non-metadata blocks.
.sp
-Default value: 1
+Default value: \fB1\fR.
.RE
.sp
pool import. Use 0 to disable and 1 to enable.
An extreme rewind import normally performs a full traversal of all
-blocks in the pool for verification. If this parameter is set to 1,
+blocks in the pool for verification. If this parameter is set to 0,
the traversal is not performed. It can be toggled once the import has
started to stop or start the traversal.
.sp
-Default value: 1
+Default value: \fB1\fR.
.RE
.sp
Maximum concurrent I/Os during the traversal performed during an "extreme
rewind" (\fB-X\fR) pool import.
.sp
-Default value: 10000
+Default value: \fB10000\fR.
.RE
.sp
less than this amount of free space, most ZPL operations (e.g. write,
create) will return ENOSPC.
.sp
-Default value: 5
+Default value: \fB5\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBvdev_removal_max_span\fR (int)
+.ad
+.RS 12n
+During top-level vdev removal, chunks of data are copied from the vdev
+which may include free space in order to trade bandwidth for IOPS.
+This parameter determines the maximum span of free space (in bytes)
+which will be included as "unnecessary" data in a chunk of copied data.
+
+The default value here was chosen to align with
+\fBzfs_vdev_read_gap_limit\fR, which is a similar concept when doing
+regular reads (but there's no reason it has to be the same).
+.sp
+Default value: \fB32,768\fR.
.RE
.sp
Default value: \fB2\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_abd_scatter_min_size\fR (uint)
+.ad
+.RS 12n
+This is the minimum allocation size that will use scatter (page-based)
+ABD's. Smaller allocations will use linear ABD's.
+.sp
+Default value: \fB1536\fR (512B and 1KB allocations will be linear).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_dnode_limit\fR (ulong)
+.ad
+.RS 12n
+When the number of bytes consumed by dnodes in the ARC exceeds this number of
+bytes, try to unpin some of it in response to demand for non-metadata. This
+value acts as a ceiling to the amount of dnode metadata, and defaults to 0 which
+indicates that a percent which is based on \fBzfs_arc_dnode_limit_percent\fR of
+the ARC meta buffers that may be used for dnodes.
+
+See also \fBzfs_arc_meta_prune\fR which serves a similar purpose but is used
+when the amount of metadata in the ARC exceeds \fBzfs_arc_meta_limit\fR rather
+than in response to overall demand for non-metadata.
+
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_dnode_limit_percent\fR (ulong)
+.ad
+.RS 12n
+Percentage that can be consumed by dnodes of ARC meta buffers.
+.sp
+See also \fBzfs_arc_dnode_limit\fR which serves a similar purpose but has a
+higher priority if set to nonzero value.
+.sp
+Default value: \fB10\fR%.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_dnode_reduce_percent\fR (ulong)
+.ad
+.RS 12n
+Percentage of ARC dnodes to try to scan in response to demand for non-metadata
+when the number of bytes consumed by dnodes exceeds \fBzfs_arc_dnode_limit\fR.
+
+.sp
+Default value: \fB10\fR% of the number of dnodes in the ARC.
+.RE
+
.sp
.ne 2
.na
\fBzfs_arc_grow_retry\fR (int)
.ad
.RS 12n
-Seconds before growing arc size
+If set to a non zero value, it will replace the arc_grow_retry value with this value.
+The arc_grow_retry value (default 5) is the number of seconds the ARC will wait before
+trying to resume growth after a memory pressure event.
.sp
-Default value: \fB5\fR.
+Default value: \fB0\fR.
.RE
.sp
Throttle I/O when free system memory drops below this percentage of total
system memory. Setting this value to 0 will disable the throttle.
.sp
-Default value: \fB10\fR.
+Default value: \fB10\fR%.
.RE
.sp
\fBzfs_arc_max\fR (ulong)
.ad
.RS 12n
-Max arc size
+Max arc size of ARC in bytes. If set to 0 then it will consume 1/2 of system
+RAM. This value must be at least 67108864 (64 megabytes).
+.sp
+This value can be changed dynamically with some caveats. It cannot be set back
+to 0 while running and reducing it below the current ARC size will not cause
+the ARC to shrink without memory pressure to induce shrinking.
.sp
Default value: \fB0\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_arc_meta_adjust_restarts\fR (ulong)
+.ad
+.RS 12n
+The number of restart passes to make while scanning the ARC attempting
+the free buffers in order to stay below the \fBzfs_arc_meta_limit\fR.
+This value should not need to be tuned but is available to facilitate
+performance analysis.
+.sp
+Default value: \fB4096\fR.
+.RE
+
.sp
.ne 2
.na
The maximum allowed size in bytes that meta data buffers are allowed to
consume in the ARC. When this limit is reached meta data buffers will
be reclaimed even if the overall arc_c_max has not been reached. This
-value defaults to 0 which indicates that 3/4 of the ARC may be used
-for meta data.
+value defaults to 0 which indicates that a percent which is based on
+\fBzfs_arc_meta_limit_percent\fR of the ARC may be used for meta data.
+.sp
+This value my be changed dynamically except that it cannot be set back to 0
+for a specific percent of the ARC; it must be set to an explicit value.
.sp
Default value: \fB0\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_arc_meta_limit_percent\fR (ulong)
+.ad
+.RS 12n
+Percentage of ARC buffers that can be used for meta data.
+
+See also \fBzfs_arc_meta_limit\fR which serves a similar purpose but has a
+higher priority if set to nonzero value.
+
+.sp
+Default value: \fB75\fR%.
+.RE
+
.sp
.ne 2
.na
.sp
.ne 2
.na
-\fBzfs_arc_meta_adjust_restarts\fR (ulong)
+\fBzfs_arc_meta_strategy\fR (int)
.ad
.RS 12n
-The number of restart passes to make while scanning the ARC attempting
-the free buffers in order to stay below the \fBzfs_arc_meta_limit\fR.
-This value should not need to be tuned but is available to facilitate
-performance analysis.
+Define the strategy for ARC meta data buffer eviction (meta reclaim strategy).
+A value of 0 (META_ONLY) will evict only the ARC meta data buffers.
+A value of 1 (BALANCED) indicates that additional data buffers may be evicted if
+that is required to in order to evict the required number of meta data buffers.
.sp
-Default value: \fB4096\fR.
+Default value: \fB1\fR.
.RE
.sp
\fBzfs_arc_min\fR (ulong)
.ad
.RS 12n
-Min arc size
+Min arc size of ARC in bytes. If set to 0 then arc_c_min will default to
+consuming the larger of 32M or 1/32 of total system memory.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_min_prefetch_ms\fR (int)
+.ad
+.RS 12n
+Minimum time prefetched blocks are locked in the ARC, specified in ms.
+A value of \fB0\fR will default to 1000 ms.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_min_prescient_prefetch_ms\fR (int)
+.ad
+.RS 12n
+Minimum time "prescient prefetched" blocks are locked in the ARC, specified
+in ms. These blocks are meant to be prefetched fairly aggresively ahead of
+the code that may use them. A value of \fB0\fR will default to 6000 ms.
.sp
-Default value: \fB100\fR.
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_arc_min_prefetch_lifespan\fR (int)
+\fBzfs_max_missing_tvds\fR (int)
.ad
.RS 12n
-Min life of prefetch block
+Number of missing top-level vdevs which will be allowed during
+pool import (only in read-only mode).
.sp
-Default value: \fB100\fR.
+Default value: \fB0\fR
.RE
.sp
.ne 2
.na
-\fBzfs_arc_num_sublists_per_state\fR (int)
+\fBzfs_multilist_num_sublists\fR (int)
.ad
.RS 12n
To allow more fine-grained locking, each ARC state contains a series
of lists for both data and meta data objects. Locking is performed at
the level of these "sub-lists". This parameters controls the number of
-sub-lists per ARC state.
+sub-lists per ARC state, and also applies to other uses of the
+multilist data structure.
.sp
-Default value: 1 or the number of on-online CPUs, whichever is greater
+Default value: \fB4\fR or the number of online CPUs, whichever is greater
.RE
.sp
\fBzfs_arc_p_min_shift\fR (int)
.ad
.RS 12n
-arc_c shift to calc min/max arc_p
+If set to a non zero value, this will update arc_p_min_shift (default 4)
+with the new value.
+arc_p_min_shift is used to shift of arc_c for calculating both min and max
+max arc_p
.sp
-Default value: \fB4\fR.
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_arc_p_aggressive_disable\fR (int)
+\fBzfs_arc_p_dampener_disable\fR (int)
.ad
.RS 12n
-Disable aggressive arc_p growth
+Disable arc_p adapt dampener
.sp
Use \fB1\fR for yes (default) and \fB0\fR to disable.
.RE
.sp
.ne 2
.na
-\fBzfs_arc_p_dampener_disable\fR (int)
+\fBzfs_arc_shrink_shift\fR (int)
.ad
.RS 12n
-Disable arc_p adapt dampener
+If set to a non zero value, this will update arc_shrink_shift (default 7)
+with the new value.
.sp
-Use \fB1\fR for yes (default) and \fB0\fR to disable.
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_arc_shrink_shift\fR (int)
+\fBzfs_arc_pc_percent\fR (uint)
.ad
.RS 12n
-log2(fraction of arc to reclaim)
+Percent of pagecache to reclaim arc to
+
+This tunable allows ZFS arc to play more nicely with the kernel's LRU
+pagecache. It can guarantee that the arc size won't collapse under scanning
+pressure on the pagecache, yet still allows arc to be reclaimed down to
+zfs_arc_min if necessary. This value is specified as percent of pagecache
+size (as measured by NR_FILE_PAGES) where that percent may exceed 100. This
+only operates during memory pressure/reclaim.
.sp
-Default value: \fB5\fR.
+Default value: \fB0\fR% (disabled).
.RE
.sp
.sp
.ne 2
.na
-\fBzfs_dbgmsg_enable\fR (int)
+\fBzfs_checksums_per_second\fR (int)
.ad
.RS 12n
-Internally ZFS keeps a small log to facilitate debugging. By default the log
-is disabled, to enable it set this option to 1. The contents of the log can
-be accessed by reading the /proc/spl/kstat/zfs/dbgmsg file. Writing 0 to
-this proc file clears the log.
+Rate limit checksum events to this many per second. Note that this should
+not be set below the zed thresholds (currently 10 checksums over 10 sec)
+or else zed may not trigger any action.
.sp
-Default value: \fB0\fR.
+Default value: 20
.RE
.sp
.ne 2
.na
-\fBzfs_dbgmsg_maxsize\fR (int)
+\fBzfs_commit_timeout_pct\fR (int)
.ad
.RS 12n
-The maximum size in bytes of the internal ZFS debug log.
+This controls the amount of time that a ZIL block (lwb) will remain "open"
+when it isn't "full", and it has a thread waiting for it to be committed to
+stable storage. The timeout is scaled based on a percentage of the last lwb
+latency to avoid significantly impacting the latency of each individual
+transaction record (itx).
.sp
-Default value: \fB4M\fR.
+Default value: \fB5\fR%.
.RE
.sp
.ne 2
.na
-\fBzfs_dbuf_state_index\fR (int)
+\fBzfs_condense_indirect_vdevs_enable\fR (int)
.ad
.RS 12n
-Calculate arc header index
+Enable condensing indirect vdev mappings. When set to a non-zero value,
+attempt to condense indirect vdev mappings if the mapping uses more than
+\fBzfs_condense_min_mapping_bytes\fR bytes of memory and if the obsolete
+space map object uses more than \fBzfs_condense_max_obsolete_bytes\fR
+bytes on-disk. The condensing process is an attempt to save memory by
+removing obsolete mappings.
.sp
-Default value: \fB0\fR.
+Default value: \fB1\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_deadman_enabled\fR (int)
+\fBzfs_condense_max_obsolete_bytes\fR (ulong)
.ad
.RS 12n
-Enable deadman timer
+Only attempt to condense indirect vdev mappings if the on-disk size
+of the obsolete space map object is greater than this number of bytes
+(see \fBfBzfs_condense_indirect_vdevs_enable\fR).
.sp
-Use \fB1\fR for yes (default) and \fB0\fR to disable.
+Default value: \fB1,073,741,824\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_deadman_synctime_ms\fR (ulong)
+\fBzfs_condense_min_mapping_bytes\fR (ulong)
.ad
.RS 12n
-Expiration time in milliseconds. This value has two meanings. First it is
-used to determine when the spa_deadman() logic should fire. By default the
-spa_deadman() will fire if spa_sync() has not completed in 1000 seconds.
-Secondly, the value determines if an I/O is considered "hung". Any I/O that
-has not completed in zfs_deadman_synctime_ms is considered "hung" resulting
-in a zevent being logged.
+Minimum size vdev mapping to attempt to condense (see
+\fBzfs_condense_indirect_vdevs_enable\fR).
.sp
-Default value: \fB1,000,000\fR.
+Default value: \fB131,072\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_dedup_prefetch\fR (int)
+\fBzfs_dbgmsg_enable\fR (int)
.ad
.RS 12n
-Enable prefetching dedup-ed blks
-.sp
-Use \fB1\fR for yes and \fB0\fR to disable (default).
-.RE
+Internally ZFS keeps a small log to facilitate debugging. By default the log
+is disabled, to enable it set this option to 1. The contents of the log can
+be accessed by reading the /proc/spl/kstat/zfs/dbgmsg file. Writing 0 to
+this proc file clears the log.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_dbgmsg_maxsize\fR (int)
+.ad
+.RS 12n
+The maximum size in bytes of the internal ZFS debug log.
+.sp
+Default value: \fB4M\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_dbuf_state_index\fR (int)
+.ad
+.RS 12n
+This feature is currently unused. It is normally used for controlling what
+reporting is available under /proc/spl/kstat/zfs.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_deadman_enabled\fR (int)
+.ad
+.RS 12n
+When a pool sync operation takes longer than \fBzfs_deadman_synctime_ms\fR
+milliseconds, or when an individual I/O takes longer than
+\fBzfs_deadman_ziotime_ms\fR milliseconds, then the operation is considered to
+be "hung". If \fBzfs_deadman_enabled\fR is set then the deadman behavior is
+invoked as described by the \fBzfs_deadman_failmode\fR module option.
+By default the deadman is enabled and configured to \fBwait\fR which results
+in "hung" I/Os only being logged. The deadman is automatically disabled
+when a pool gets suspended.
+.sp
+Default value: \fB1\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_deadman_failmode\fR (charp)
+.ad
+.RS 12n
+Controls the failure behavior when the deadman detects a "hung" I/O. Valid
+values are \fBwait\fR, \fBcontinue\fR, and \fBpanic\fR.
+.sp
+\fBwait\fR - Wait for a "hung" I/O to complete. For each "hung" I/O a
+"deadman" event will be posted describing that I/O.
+.sp
+\fBcontinue\fR - Attempt to recover from a "hung" I/O by re-dispatching it
+to the I/O pipeline if possible.
+.sp
+\fBpanic\fR - Panic the system. This can be used to facilitate an automatic
+fail-over to a properly configured fail-over partner.
+.sp
+Default value: \fBwait\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_deadman_checktime_ms\fR (int)
+.ad
+.RS 12n
+Check time in milliseconds. This defines the frequency at which we check
+for hung I/O and potentially invoke the \fBzfs_deadman_failmode\fR behavior.
+.sp
+Default value: \fB60,000\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_deadman_synctime_ms\fR (ulong)
+.ad
+.RS 12n
+Interval in milliseconds after which the deadman is triggered and also
+the interval after which a pool sync operation is considered to be "hung".
+Once this limit is exceeded the deadman will be invoked every
+\fBzfs_deadman_checktime_ms\fR milliseconds until the pool sync completes.
+.sp
+Default value: \fB600,000\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_deadman_ziotime_ms\fR (ulong)
+.ad
+.RS 12n
+Interval in milliseconds after which the deadman is triggered and an
+individual I/O operation is considered to be "hung". As long as the I/O
+remains "hung" the deadman will be invoked every \fBzfs_deadman_checktime_ms\fR
+milliseconds until the I/O completes.
+.sp
+Default value: \fB300,000\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_dedup_prefetch\fR (int)
+.ad
+.RS 12n
+Enable prefetching dedup-ed blks
+.sp
+Use \fB1\fR for yes and \fB0\fR to disable (default).
+.RE
.sp
.ne 2
This value should be >= zfs_vdev_async_write_active_max_dirty_percent.
See the section "ZFS TRANSACTION DELAY".
.sp
-Default value: \fB60\fR.
+Default value: \fB60\fR%.
.RE
.sp
Default value: \fB500,000\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_slow_io_events_per_second\fR (int)
+.ad
+.RS 12n
+Rate limit delay zevents (which report slow I/Os) to this many per second.
+.sp
+Default value: 20
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_unlink_suspend_progress\fR (uint)
+.ad
+.RS 12n
+When enabled, files will not be asynchronously removed from the list of pending
+unlinks and the space they consume will be leaked. Once this option has been
+disabled and the dataset is remounted, the pending unlinks will be processed
+and the freed space returned to the pool.
+This option is used by the test suite to facilitate testing.
+.sp
+Uses \fB0\fR (default) to allow progress and \fB1\fR to pause progress.
+.RE
+
.sp
.ne 2
.na
over \fBzfs_dirty_data_max_percent\fR.
See the section "ZFS TRANSACTION DELAY".
.sp
-Default value: 10 percent of all memory, capped at \fBzfs_dirty_data_max_max\fR.
+Default value: \fB10\fR% of physical RAM, capped at \fBzfs_dirty_data_max_max\fR.
.RE
.sp
precedence over \fBzfs_dirty_data_max_max_percent\fR. See the section
"ZFS TRANSACTION DELAY".
.sp
-Default value: 25% of physical RAM.
+Default value: \fB25\fR% of physical RAM.
.RE
.sp
The parameter \fBzfs_dirty_data_max_max\fR takes precedence over this
one. See the section "ZFS TRANSACTION DELAY".
.sp
-Default value: 25
+Default value: \fB25\fR%.
.RE
.sp
up. The parameter \fBzfs_dirty_data_max\fR takes precedence over this
one. See the section "ZFS TRANSACTION DELAY".
.sp
-Default value: 10%, subject to \fBzfs_dirty_data_max_max\fR.
+Default value: \fB10\fR%, subject to \fBzfs_dirty_data_max_max\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_dirty_data_sync_percent\fR (int)
+.ad
+.RS 12n
+Start syncing out a transaction group if there's at least this much dirty data
+as a percentage of \fBzfs_dirty_data_max\fR. This should be less than
+\fBzfs_vdev_async_write_active_min_dirty_percent\fR.
+.sp
+Default value: \fB20\fR% of \fBzfs_dirty_data_max\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_dirty_data_sync\fR (int)
+\fBzfs_fletcher_4_impl\fR (string)
.ad
.RS 12n
-Start syncing out a transaction group if there is at least this much dirty data.
+Select a fletcher 4 implementation.
+.sp
+Supported selectors are: \fBfastest\fR, \fBscalar\fR, \fBsse2\fR, \fBssse3\fR,
+\fBavx2\fR, \fBavx512f\fR, and \fBaarch64_neon\fR.
+All of the selectors except \fBfastest\fR and \fBscalar\fR require instruction
+set extensions to be available and will only appear if ZFS detects that they are
+present at runtime. If multiple implementations of fletcher 4 are available,
+the \fBfastest\fR will be chosen using a micro benchmark. Selecting \fBscalar\fR
+results in the original, CPU based calculation, being used. Selecting any option
+other than \fBfastest\fR and \fBscalar\fR results in vector instructions from
+the respective CPU instruction set being used.
.sp
-Default value: \fB67,108,864\fR.
+Default value: \fBfastest\fR.
.RE
.sp
.sp
.ne 2
.na
-\fBzfs_free_max_blocks\fR (ulong)
+\fBzfs_async_block_max_blocks\fR (ulong)
.ad
.RS 12n
Maximum number of blocks freed in a single txg.
Default value: \fB100,000\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_override_estimate_recordsize\fR (ulong)
+.ad
+.RS 12n
+Record size calculation override for zfs send estimates.
+.sp
+Default value: \fB0\fR.
+.RE
+
.sp
.ne 2
.na
\fBzfs_vdev_async_read_max_active\fR (int)
.ad
.RS 12n
-Maxium asynchronous read I/Os active to each device.
+Maximum asynchronous read I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
.sp
Default value: \fB3\fR.
the dirty data is between min and max, the active I/O limit is linearly
interpolated. See the section "ZFS I/O SCHEDULER".
.sp
-Default value: \fB60\fR.
+Default value: \fB60\fR%.
.RE
.sp
the dirty data is between min and max, the active I/O limit is linearly
interpolated. See the section "ZFS I/O SCHEDULER".
.sp
-Default value: \fB30\fR.
+Default value: \fB30\fR%.
.RE
.sp
\fBzfs_vdev_async_write_max_active\fR (int)
.ad
.RS 12n
-Maxium asynchronous write I/Os active to each device.
+Maximum asynchronous write I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
.sp
Default value: \fB10\fR.
Minimum asynchronous write I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
.sp
+Lower values are associated with better latency on rotational media but poorer
+resilver performance. The default value of 2 was chosen as a compromise. A
+value of 3 has been shown to improve resilver performance further at a cost of
+further increasing latency.
+.sp
+Default value: \fB2\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_initializing_max_active\fR (int)
+.ad
+.RS 12n
+Maximum initializing I/Os active to each device.
+See the section "ZFS I/O SCHEDULER".
+.sp
+Default value: \fB1\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_initializing_min_active\fR (int)
+.ad
+.RS 12n
+Minimum initializing I/Os active to each device.
+See the section "ZFS I/O SCHEDULER".
+.sp
Default value: \fB1\fR.
.RE
Default value: \fB1,000\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_vdev_removal_max_active\fR (int)
+.ad
+.RS 12n
+Maximum removal I/Os active to each device.
+See the section "ZFS I/O SCHEDULER".
+.sp
+Default value: \fB2\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_removal_min_active\fR (int)
+.ad
+.RS 12n
+Minimum removal I/Os active to each device.
+See the section "ZFS I/O SCHEDULER".
+.sp
+Default value: \fB1\fR.
+.RE
+
.sp
.ne 2
.na
\fBzfs_vdev_scrub_max_active\fR (int)
.ad
.RS 12n
-Maxium scrub I/Os active to each device.
+Maximum scrub I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
.sp
Default value: \fB2\fR.
\fBzfs_vdev_sync_read_max_active\fR (int)
.ad
.RS 12n
-Maxium synchronous read I/Os active to each device.
+Maximum synchronous read I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
.sp
Default value: \fB10\fR.
\fBzfs_vdev_sync_write_max_active\fR (int)
.ad
.RS 12n
-Maxium synchronous write I/Os active to each device.
+Maximum synchronous write I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
.sp
Default value: \fB10\fR.
.sp
.ne 2
.na
-\fBzfs_disable_dup_eviction\fR (int)
+\fBzfs_vdev_trim_max_active\fR (int)
.ad
.RS 12n
-Disable duplicate buffer eviction
+Maximum trim/discard I/Os active to each device.
+See the section "ZFS I/O SCHEDULER".
.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
+Default value: \fB2\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_trim_min_active\fR (int)
+.ad
+.RS 12n
+Minimum trim/discard I/Os active to each device.
+See the section "ZFS I/O SCHEDULER".
+.sp
+Default value: \fB1\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_queue_depth_pct\fR (int)
+.ad
+.RS 12n
+Maximum number of queued allocations per top-level vdev expressed as
+a percentage of \fBzfs_vdev_async_write_max_active\fR which allows the
+system to detect devices that are more capable of handling allocations
+and to allocate more blocks to those devices. It allows for dynamic
+allocation distribution when devices are imbalanced as fuller devices
+will tend to be slower than empty devices.
+
+See also \fBzio_dva_throttle_enabled\fR.
+.sp
+Default value: \fB1000\fR%.
.RE
.sp
16 ZFS_DEBUG_MODIFY
Check for illegally modified ARC buffers.
_
-32 ZFS_DEBUG_SPA
- Enable spa_dbgmsg entries in the debug log.
-_
64 ZFS_DEBUG_ZIO_FREE
Enable verification of block frees.
_
128 ZFS_DEBUG_HISTOGRAM_VERIFY
Enable extra spacemap histogram verifications.
+_
+256 ZFS_DEBUG_METASLAB_VERIFY
+ Verify space accounting on disk matches in-core range_trees.
+_
+512 ZFS_DEBUG_SET_ERROR
+ Enable SET_ERROR and dprintf entries in the debug log.
+_
+1024 ZFS_DEBUG_INDIRECT_REMAP
+ Verify split blocks created by device removal.
+_
+2048 ZFS_DEBUG_TRIM
+ Verify TRIM ranges are always within the allocatable range tree.
.TE
.sp
* Requires debug build.
\fBzfs_free_min_time_ms\fR (int)
.ad
.RS 12n
-Min millisecs to free per txg
+During a \fBzfs destroy\fR operation using \fBfeature@async_destroy\fR a minimum
+of this much time will be spent working on freeing blocks per txg.
.sp
Default value: \fB1,000\fR.
.RE
\fBzfs_immediate_write_sz\fR (long)
.ad
.RS 12n
-Largest data block to write to zil
+Largest data block to write to zil. Larger blocks will be treated as if the
+dataset being written to had the property setting \fBlogbias=throughput\fR.
.sp
Default value: \fB32,768\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_initialize_value\fR (ulong)
+.ad
+.RS 12n
+Pattern written to vdev free space by \fBzpool initialize\fR.
+.sp
+Default value: \fB16,045,690,984,833,335,022\fR (0xdeadbeefdeadbeee).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_lua_max_instrlimit\fR (ulong)
+.ad
+.RS 12n
+The maximum execution time limit that can be set for a ZFS channel program,
+specified as a number of Lua instructions.
+.sp
+Default value: \fB100,000,000\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_lua_max_memlimit\fR (ulong)
+.ad
+.RS 12n
+The maximum memory limit that can be set for a ZFS channel program, specified
+in bytes.
+.sp
+Default value: \fB104,857,600\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_max_dataset_nesting\fR (int)
+.ad
+.RS 12n
+The maximum depth of nested datasets. This value can be tuned temporarily to
+fix existing datasets that exceed the predefined limit.
+.sp
+Default value: \fB50\fR.
+.RE
+
.sp
.ne 2
.na
.ad
.RS 12n
We currently support block sizes from 512 bytes to 16MB. The benefits of
-larger blocks, and thus larger IO, need to be weighed against the cost of
+larger blocks, and thus larger I/O, need to be weighed against the cost of
COWing a giant block to modify one byte. Additionally, very large blocks
can have an impact on i/o latency, and also potentially on the memory
allocator. Therefore, we do not allow the recordsize to be set larger than
Default value: \fB1,048,576\fR.
.RE
-.sp
-.ne 2
-.na
-\fBzfs_mdcomp_disable\fR (int)
-.ad
-.RS 12n
-Disable meta data compression
-.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
-.RE
-
.sp
.ne 2
.na
.ad
.RS 12n
Metaslab groups are considered eligible for allocations if their
-fragmenation metric (measured as a percentage) is less than or equal to
+fragmentation metric (measured as a percentage) is less than or equal to
this value. If a metaslab group exceeds this threshold then it will be
skipped unless all metaslab groups within the metaslab class have also
crossed this threshold.
allocations. The default value of 0 disables the feature and causes
all metaslab groups to be eligible for allocations.
-This parameter allows to deal with pools having heavily imbalanced
+This parameter allows one to deal with pools having heavily imbalanced
vdevs such as would be the case when a new vdev has been added.
Setting the threshold to a non-zero percentage will stop allocations
from being made to vdevs that aren't filled to the specified percentage
.sp
.ne 2
.na
-\fBzfs_no_scrub_io\fR (int)
+\fBzfs_ddt_data_is_special\fR (int)
.ad
.RS 12n
-Set for no scrub I/O
+If enabled, ZFS will place DDT data into the special allocation class.
.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
+Default value: \fB1\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_no_scrub_prefetch\fR (int)
+\fBzfs_user_indirect_is_special\fR (int)
.ad
.RS 12n
-Set for no scrub prefetching
+If enabled, ZFS will place user data (both file and zvol) indirect blocks
+into the special allocation class.
.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
+Default value: \fB1\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_nocacheflush\fR (int)
+\fBzfs_multihost_history\fR (int)
.ad
.RS 12n
-Disable cache flushes
+Historical statistics for the last N multihost updates will be available in
+\fB/proc/spl/kstat/zfs/<pool>/multihost\fR
.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_nopwrite_enabled\fR (int)
+\fBzfs_multihost_interval\fR (ulong)
.ad
.RS 12n
-Enable NOP writes
+Used to control the frequency of multihost writes which are performed when the
+\fBmultihost\fR pool property is on. This is one factor used to determine the
+length of the activity check during import.
.sp
-Use \fB1\fR for yes (default) and \fB0\fR to disable.
+The multihost write period is \fBzfs_multihost_interval / leaf-vdevs\fR
+milliseconds. On average a multihost write will be issued for each leaf vdev
+every \fBzfs_multihost_interval\fR milliseconds. In practice, the observed
+period can vary with the I/O load and this observed value is the delay which is
+stored in the uberblock.
+.sp
+Default value: \fB1000\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_pd_bytes_max\fR (int)
+\fBzfs_multihost_import_intervals\fR (uint)
.ad
.RS 12n
-The number of bytes which should be prefetched.
+Used to control the duration of the activity test on import. Smaller values of
+\fBzfs_multihost_import_intervals\fR will reduce the import time but increase
+the risk of failing to detect an active pool. The total activity check time is
+never allowed to drop below one second.
.sp
-Default value: \fB52,428,800\fR.
+On import the activity check waits a minimum amount of time determined by
+\fBzfs_multihost_interval * zfs_multihost_import_intervals\fR, or the same
+product computed on the host which last had the pool imported (whichever is
+greater). The activity check time may be further extended if the value of mmp
+delay found in the best uberblock indicates actual multihost updates happened
+at longer intervals than \fBzfs_multihost_interval\fR. A minimum value of
+\fB100ms\fR is enforced.
+.sp
+A value of 0 is ignored and treated as if it was set to 1.
+.sp
+Default value: \fB20\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_prefetch_disable\fR (int)
+\fBzfs_multihost_fail_intervals\fR (uint)
.ad
.RS 12n
-This tunable disables predictive prefetch. Note that it leaves "prescient"
-prefetch (e.g. prefetch for zfs send) intact. Unlike predictive prefetch,
-prescient prefetch never issues i/os that end up not being needed, so it
-can't hurt performance.
+Controls the behavior of the pool when multihost write failures or delays are
+detected.
.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
-.RE
+When \fBzfs_multihost_fail_intervals = 0\fR, multihost write failures or delays
+are ignored. The failures will still be reported to the ZED which depending on
+its configuration may take action such as suspending the pool or offlining a
+device.
.sp
-.ne 2
-.na
-\fBzfs_read_chunk_size\fR (long)
+When \fBzfs_multihost_fail_intervals > 0\fR, the pool will be suspended if
+\fBzfs_multihost_fail_intervals * zfs_multihost_interval\fR milliseconds pass
+without a successful mmp write. This guarantees the activity test will see
+mmp writes if the pool is imported. A value of 1 is ignored and treated as
+if it was set to 2. This is necessary to prevent the pool from being suspended
+due to normal, small I/O latency variations.
+
+.sp
+Default value: \fB10\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_no_scrub_io\fR (int)
+.ad
+.RS 12n
+Set for no scrub I/O. This results in scrubs not actually scrubbing data and
+simply doing a metadata crawl of the pool instead.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_no_scrub_prefetch\fR (int)
+.ad
+.RS 12n
+Set to disable block prefetching for scrubs.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_nocacheflush\fR (int)
+.ad
+.RS 12n
+Disable cache flush operations on disks when writing. Setting this will
+cause pool corruption on power loss if a volatile out-of-order write cache
+is enabled.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_nopwrite_enabled\fR (int)
+.ad
+.RS 12n
+Enable NOP writes
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR to disable.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_dmu_offset_next_sync\fR (int)
+.ad
+.RS 12n
+Enable forcing txg sync to find holes. When enabled forces ZFS to act
+like prior versions when SEEK_HOLE or SEEK_DATA flags are used, which
+when a dnode is dirty causes txg's to be synced so that this data can be
+found.
+.sp
+Use \fB1\fR for yes and \fB0\fR to disable (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_pd_bytes_max\fR (int)
+.ad
+.RS 12n
+The number of bytes which should be prefetched during a pool traversal
+(eg: \fBzfs send\fR or other data crawling operations)
+.sp
+Default value: \fB52,428,800\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_per_txg_dirty_frees_percent \fR (ulong)
+.ad
+.RS 12n
+Tunable to control percentage of dirtied indirect blocks from frees allowed
+into one TXG. After this threshold is crossed, additional frees will wait until
+the next TXG.
+A value of zero will disable this throttle.
+.sp
+Default value: \fB5\fR, set to \fB0\fR to disable.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_prefetch_disable\fR (int)
+.ad
+.RS 12n
+This tunable disables predictive prefetch. Note that it leaves "prescient"
+prefetch (e.g. prefetch for zfs send) intact. Unlike predictive prefetch,
+prescient prefetch never issues i/os that end up not being needed, so it
+can't hurt performance.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_qat_checksum_disable\fR (int)
+.ad
+.RS 12n
+This tunable disables qat hardware acceleration for sha256 checksums. It
+may be set after the zfs modules have been loaded to initialize the qat
+hardware as long as support is compiled in and the qat driver is present.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_qat_compress_disable\fR (int)
+.ad
+.RS 12n
+This tunable disables qat hardware acceleration for gzip compression. It
+may be set after the zfs modules have been loaded to initialize the qat
+hardware as long as support is compiled in and the qat driver is present.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_qat_encrypt_disable\fR (int)
+.ad
+.RS 12n
+This tunable disables qat hardware acceleration for AES-GCM encryption. It
+may be set after the zfs modules have been loaded to initialize the qat
+hardware as long as support is compiled in and the qat driver is present.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_read_chunk_size\fR (long)
.ad
.RS 12n
Bytes to read per chunk
\fBzfs_read_history\fR (int)
.ad
.RS 12n
-Historic statistics for the last N reads
+Historical statistics for the last N reads will be available in
+\fB/proc/spl/kstat/zfs/<pool>/reads\fR
.sp
-Default value: \fB0\fR.
+Default value: \fB0\fR (no data is kept).
.RE
.sp
Use \fB1\fR for yes and \fB0\fR for no (default).
.RE
+.sp
+.ne 2
+.na
+\fBzfs_reconstruct_indirect_combinations_max\fR (int)
+.ad
+.RS 12na
+If an indirect split block contains more than this many possible unique
+combinations when being reconstructed, consider it too computationally
+expensive to check them all. Instead, try at most
+\fBzfs_reconstruct_indirect_combinations_max\fR randomly-selected
+combinations each time the block is accessed. This allows all segment
+copies to participate fairly in the reconstruction when all combinations
+cannot be checked and prevents repeated use of one bad copy.
+.sp
+Default value: \fB4096\fR.
+.RE
+
.sp
.ne 2
.na
.sp
.ne 2
.na
-\fBzfs_resilver_delay\fR (int)
+\fBzfs_removal_ignore_errors\fR (int)
.ad
.RS 12n
-Number of ticks to delay prior to issuing a resilver I/O operation when
-a non-resilver or non-scrub I/O operation has occurred within the past
-\fBzfs_scan_idle\fR ticks.
.sp
-Default value: \fB2\fR.
+Ignore hard IO errors during device removal. When set, if a device encounters
+a hard IO error during the removal process the removal will not be cancelled.
+This can result in a normally recoverable block becoming permanently damaged
+and is not recommended. This should only be used as a last resort when the
+pool cannot be returned to a healthy state prior to removing the device.
+.sp
+Default value: \fB0\fR.
.RE
.sp
\fBzfs_resilver_min_time_ms\fR (int)
.ad
.RS 12n
-Min millisecs to resilver per txg
+Resilvers are processed by the sync thread. While resilvering it will spend
+at least this much time working on a resilver between txg flushes.
.sp
Default value: \fB3,000\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_scan_idle\fR (int)
+\fBzfs_scan_ignore_errors\fR (int)
.ad
.RS 12n
-Idle window in clock ticks. During a scrub or a resilver, if
-a non-scrub or non-resilver I/O operation has occurred during this
-window, the next scrub or resilver operation is delayed by, respectively
-\fBzfs_scrub_delay\fR or \fBzfs_resilver_delay\fR ticks.
+If set to a nonzero value, remove the DTL (dirty time list) upon
+completion of a pool scan (scrub) even if there were unrepairable
+errors. It is intended to be used during pool repair or recovery to
+stop resilvering when the pool is next imported.
.sp
-Default value: \fB50\fR.
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_scan_min_time_ms\fR (int)
+\fBzfs_scrub_min_time_ms\fR (int)
.ad
.RS 12n
-Min millisecs to scrub per txg
+Scrubs are processed by the sync thread. While scrubbing it will spend
+at least this much time working on a scrub between txg flushes.
.sp
Default value: \fB1,000\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_scrub_delay\fR (int)
+\fBzfs_scan_checkpoint_intval\fR (int)
.ad
.RS 12n
-Number of ticks to delay prior to issuing a scrub I/O operation when
-a non-scrub or non-resilver I/O operation has occurred within the past
-\fBzfs_scan_idle\fR ticks.
+To preserve progress across reboots the sequential scan algorithm periodically
+needs to stop metadata scanning and issue all the verifications I/Os to disk.
+The frequency of this flushing is determined by the
+\fBzfs_scan_checkpoint_intval\fR tunable.
.sp
-Default value: \fB4\fR.
+Default value: \fB7200\fR seconds (every 2 hours).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_fill_weight\fR (int)
+.ad
+.RS 12n
+This tunable affects how scrub and resilver I/O segments are ordered. A higher
+number indicates that we care more about how filled in a segment is, while a
+lower number indicates we care more about the size of the extent without
+considering the gaps within a segment. This value is only tunable upon module
+insertion. Changing the value afterwards will have no affect on scrub or
+resilver performance.
+.sp
+Default value: \fB3\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_issue_strategy\fR (int)
+.ad
+.RS 12n
+Determines the order that data will be verified while scrubbing or resilvering.
+If set to \fB1\fR, data will be verified as sequentially as possible, given the
+amount of memory reserved for scrubbing (see \fBzfs_scan_mem_lim_fact\fR). This
+may improve scrub performance if the pool's data is very fragmented. If set to
+\fB2\fR, the largest mostly-contiguous chunk of found data will be verified
+first. By deferring scrubbing of small segments, we may later find adjacent data
+to coalesce and increase the segment size. If set to \fB0\fR, zfs will use
+strategy \fB1\fR during normal verification and strategy \fB2\fR while taking a
+checkpoint.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_legacy\fR (int)
+.ad
+.RS 12n
+A value of 0 indicates that scrubs and resilvers will gather metadata in
+memory before issuing sequential I/O. A value of 1 indicates that the legacy
+algorithm will be used where I/O is initiated as soon as it is discovered.
+Changing this value to 0 will not affect scrubs or resilvers that are already
+in progress.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_max_ext_gap\fR (int)
+.ad
+.RS 12n
+Indicates the largest gap in bytes between scrub / resilver I/Os that will still
+be considered sequential for sorting purposes. Changing this value will not
+affect scrubs or resilvers that are already in progress.
+.sp
+Default value: \fB2097152 (2 MB)\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_mem_lim_fact\fR (int)
+.ad
+.RS 12n
+Maximum fraction of RAM used for I/O sorting by sequential scan algorithm.
+This tunable determines the hard limit for I/O sorting memory usage.
+When the hard limit is reached we stop scanning metadata and start issuing
+data verification I/O. This is done until we get below the soft limit.
+.sp
+Default value: \fB20\fR which is 5% of RAM (1/20).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_mem_lim_soft_fact\fR (int)
+.ad
+.RS 12n
+The fraction of the hard limit used to determined the soft limit for I/O sorting
+by the sequential scan algorithm. When we cross this limit from bellow no action
+is taken. When we cross this limit from above it is because we are issuing
+verification I/O. In this case (unless the metadata scan is done) we stop
+issuing verification I/O and start scanning metadata again until we get to the
+hard limit.
+.sp
+Default value: \fB20\fR which is 5% of the hard limit (1/20).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_vdev_limit\fR (int)
+.ad
+.RS 12n
+Maximum amount of data that can be concurrently issued at once for scrubs and
+resilvers per leaf device, given in bytes.
+.sp
+Default value: \fB41943040\fR.
.RE
.sp
\fBzfs_send_corrupt_data\fR (int)
.ad
.RS 12n
-Allow to send corrupt data (ignore read/checksum errors when sending data)
+Allow sending of corrupt data (ignore read/checksum errors when sending data)
.sp
Use \fB1\fR for yes and \fB0\fR for no (default).
.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.
+.sp
+Default value: \fB16,777,216\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_recv_queue_length\fR (int)
+.ad
+.RS 12n
+.sp
+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_sync_pass_deferred_free\fR (int)
.ad
.RS 12n
-Defer frees starting in this pass
+Flushing of data to disk is done in passes. Defer frees starting in this pass
.sp
Default value: \fB2\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_spa_discard_memory_limit\fR (int)
+.ad
+.RS 12n
+Maximum memory used for prefetching a checkpoint's space map on each
+vdev while discarding the checkpoint.
+.sp
+Default value: \fB16,777,216\fR.
+.RE
+
.sp
.ne 2
.na
\fBzfs_sync_pass_rewrite\fR (int)
.ad
.RS 12n
-Rewrite new bps starting in this pass
+Rewrite new block pointers starting in this pass
.sp
Default value: \fB2\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_top_maxinflight\fR (int)
+\fBzfs_sync_taskq_batch_pct\fR (int)
.ad
.RS 12n
-Max I/Os per top-level vdev during scrub or resilver operations.
+This controls the number of threads used by the dp_sync_taskq. The default
+value of 75% will create a maximum of one thread per cpu.
+.sp
+Default value: \fB75\fR%.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_trim_extent_bytes_max\fR (unsigned int)
+.ad
+.RS 12n
+Maximum size of TRIM command. Ranges larger than this will be split in to
+chunks no larger than \fBzfs_trim_extent_bytes_max\fR bytes before being
+issued to the device.
+.sp
+Default value: \fB134,217,728\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_trim_extent_bytes_min\fR (unsigned int)
+.ad
+.RS 12n
+Minimum size of TRIM commands. TRIM ranges smaller than this will be skipped
+unless they're part of a larger range which was broken in to chunks. This is
+done because it's common for these small TRIMs to negatively impact overall
+performance. This value can be set to 0 to TRIM all unallocated space.
+.sp
+Default value: \fB32,768\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_trim_metaslab_skip\fR (unsigned int)
+.ad
+.RS 12n
+Skip uninitialized metaslabs during the TRIM process. This option is useful
+for pools constructed from large thinly-provisioned devices where TRIM
+operations are slow. As a pool ages an increasing fraction of the pools
+metaslabs will be initialized progressively degrading the usefulness of
+this option. This setting is stored when starting a manual TRIM and will
+persist for the duration of the requested TRIM.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_trim_queue_limit\fR (unsigned int)
+.ad
+.RS 12n
+Maximum number of queued TRIMs outstanding per leaf vdev. The number of
+concurrent TRIM commands issued to the device is controlled by the
+\fBzfs_vdev_trim_min_active\fR and \fBzfs_vdev_trim_max_active\fR module
+options.
+.sp
+Default value: \fB10\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_trim_txg_batch\fR (unsigned int)
+.ad
+.RS 12n
+The number of transaction groups worth of frees which should be aggregated
+before TRIM operations are issued to the device. This setting represents a
+trade-off between issuing larger, more efficient TRIM operations and the
+delay before the recently trimmed space is available for use by the device.
+.sp
+Increasing this value will allow frees to be aggregated for a longer time.
+This will result is larger TRIM operations and potentially increased memory
+usage. Decreasing this value will have the opposite effect. The default
+value of 32 was determined to be a reasonable compromise.
.sp
Default value: \fB32\fR.
.RE
\fBzfs_txg_history\fR (int)
.ad
.RS 12n
-Historic statistics for the last N txgs
+Historical statistics for the last N txgs will be available in
+\fB/proc/spl/kstat/zfs/<pool>/txgs\fR
.sp
Default value: \fB0\fR.
.RE
\fBzfs_txg_timeout\fR (int)
.ad
.RS 12n
-Max seconds worth of delta per txg
+Flush dirty data to disk at least every N seconds (maximum txg duration)
.sp
Default value: \fB5\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_vdev_aggregate_trim\fR (int)
+.ad
+.RS 12n
+Allow TRIM I/Os to be aggregated. This is normally not helpful because
+the extents to be trimmed will have been already been aggregated by the
+metaslab. This option is provided for debugging and performance analysis.
+.sp
+Default value: \fB0\fR.
+.RE
+
.sp
.ne 2
.na
.RS 12n
Max vdev I/O aggregation size
.sp
+Default value: \fB1,048,576\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_aggregation_limit_non_rotating\fR (int)
+.ad
+.RS 12n
+Max vdev I/O aggregation size for non-rotating media
+.sp
Default value: \fB131,072\fR.
.RE
.RS 12n
Shift size to inflate reads too
.sp
-Default value: \fB16\fR.
+Default value: \fB16\fR (effectively 65536).
.RE
.sp
\fBzfs_vdev_cache_max\fR (int)
.ad
.RS 12n
-Inflate reads small than max
+Inflate reads smaller than this value to meet the \fBzfs_vdev_cache_bshift\fR
+size (default 64k).
+.sp
+Default value: \fB16384\fR.
.RE
.sp
\fBzfs_vdev_cache_size\fR (int)
.ad
.RS 12n
-Total size of the per-disk cache
+Total size of the per-disk cache in bytes.
+.sp
+Currently this feature is disabled as it has been found to not be helpful
+for performance and in some cases harmful.
.sp
Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_vdev_mirror_switch_us\fR (int)
+\fBzfs_vdev_mirror_rotating_inc\fR (int)
.ad
.RS 12n
-Switch mirrors every N usecs
+A number by which the balancing algorithm increments the load calculation for
+the purpose of selecting the least busy mirror member when an I/O immediately
+follows its predecessor on rotational vdevs for the purpose of making decisions
+based on load.
.sp
-Default value: \fB10,000\fR.
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_mirror_rotating_seek_inc\fR (int)
+.ad
+.RS 12n
+A number by which the balancing algorithm increments the load calculation for
+the purpose of selecting the least busy mirror member when an I/O lacks
+locality as defined by the zfs_vdev_mirror_rotating_seek_offset. I/Os within
+this that are not immediately following the previous I/O are incremented by
+half.
+.sp
+Default value: \fB5\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_mirror_rotating_seek_offset\fR (int)
+.ad
+.RS 12n
+The maximum distance for the last queued I/O in which the balancing algorithm
+considers an I/O to have locality.
+See the section "ZFS I/O SCHEDULER".
+.sp
+Default value: \fB1048576\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_mirror_non_rotating_inc\fR (int)
+.ad
+.RS 12n
+A number by which the balancing algorithm increments the load calculation for
+the purpose of selecting the least busy mirror member on non-rotational vdevs
+when I/Os do not immediately follow one another.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_vdev_mirror_non_rotating_seek_inc\fR (int)
+.ad
+.RS 12n
+A number by which the balancing algorithm increments the load calculation for
+the purpose of selecting the least busy mirror member when an I/O lacks
+locality as defined by the zfs_vdev_mirror_rotating_seek_offset. I/Os within
+this that are not immediately following the previous I/O are incremented by
+half.
+.sp
+Default value: \fB1\fR.
.RE
.sp
\fBzfs_vdev_read_gap_limit\fR (int)
.ad
.RS 12n
-Aggregate read I/O over gap
+Aggregate read I/O operations if the gap on-disk between them is within this
+threshold.
.sp
Default value: \fB32,768\fR.
.RE
\fBzfs_vdev_scheduler\fR (charp)
.ad
.RS 12n
-I/O scheduler
+Set the Linux I/O scheduler on whole disk vdevs to this scheduler. Valid options
+are noop, cfq, bfq & deadline
.sp
Default value: \fBnoop\fR.
.RE
Default value: \fB4,096\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_vdev_raidz_impl\fR (string)
+.ad
+.RS 12n
+Parameter for selecting raidz parity implementation to use.
+
+Options marked (always) below may be selected on module load as they are
+supported on all systems.
+The remaining options may only be set after the module is loaded, as they
+are available only if the implementations are compiled in and supported
+on the running system.
+
+Once the module is loaded, the content of
+/sys/module/zfs/parameters/zfs_vdev_raidz_impl will show available options
+with the currently selected one enclosed in [].
+Possible options are:
+ fastest - (always) implementation selected using built-in benchmark
+ original - (always) original raidz implementation
+ scalar - (always) scalar raidz implementation
+ sse2 - implementation using SSE2 instruction set (64bit x86 only)
+ ssse3 - implementation using SSSE3 instruction set (64bit x86 only)
+ avx2 - implementation using AVX2 instruction set (64bit x86 only)
+ avx512f - implementation using AVX512F instruction set (64bit x86 only)
+ avx512bw - implementation using AVX512F & AVX512BW instruction sets (64bit x86 only)
+ aarch64_neon - implementation using NEON (Aarch64/64 bit ARMv8 only)
+ aarch64_neonx2 - implementation using NEON with more unrolling (Aarch64/64 bit ARMv8 only)
+.sp
+Default value: \fBfastest\fR.
+.RE
+
.sp
.ne 2
.na
\fBzfs_zevent_cols\fR (int)
.ad
.RS 12n
-Max event column width
+When zevents are logged to the console use this as the word wrap width.
.sp
Default value: \fB80\fR.
.RE
\fBzfs_zevent_len_max\fR (int)
.ad
.RS 12n
-Max event queue length
+Max event queue length. A value of 0 will result in a calculated value which
+increases with the number of CPUs in the system (minimum 64 events). Events
+in the queue can be viewed with the \fBzpool events\fR command.
.sp
Default value: \fB0\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_zil_clean_taskq_maxalloc\fR (int)
+.ad
+.RS 12n
+The maximum number of taskq entries that are allowed to be cached. When this
+limit is exceeded transaction records (itxs) will be cleaned synchronously.
+.sp
+Default value: \fB1048576\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_zil_clean_taskq_minalloc\fR (int)
+.ad
+.RS 12n
+The number of taskq entries that are pre-populated when the taskq is first
+created and are immediately available for use.
+.sp
+Default value: \fB1024\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_zil_clean_taskq_nthr_pct\fR (int)
+.ad
+.RS 12n
+This controls the number of threads used by the dp_zil_clean_taskq. The default
+value of 100% will create a maximum of one thread per cpu.
+.sp
+Default value: \fB100\fR%.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzil_nocacheflush\fR (int)
+.ad
+.RS 12n
+Disable the cache flush commands that are normally sent to the disk(s) by
+the ZIL after an LWB write has completed. Setting this will cause ZIL
+corruption on power loss if a volatile out-of-order write cache is enabled.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
.sp
.ne 2
.na
\fBzil_replay_disable\fR (int)
.ad
.RS 12n
-Disable intent logging replay
+Disable intent logging replay. Can be disabled for recovery from corrupted
+ZIL
.sp
Use \fB1\fR for yes and \fB0\fR for no (default).
.RE
.sp
.ne 2
.na
-\fBzil_slog_limit\fR (ulong)
+\fBzil_slog_bulk\fR (ulong)
.ad
.RS 12n
-Max commit bytes to separate log device
+Limit SLOG write size per commit executed with synchronous priority.
+Any writes above that will be executed with lower (asynchronous) priority
+to limit potential SLOG device abuse by single active ZIL writer.
.sp
-Default value: \fB1,048,576\fR.
+Default value: \fB786,432\fR.
.RE
.sp
.ne 2
.na
-\fBzio_delay_max\fR (int)
+\fBzio_deadman_log_all\fR (int)
.ad
.RS 12n
-Max zio millisecond delay before posting event
+If non-zero, the zio deadman will produce debugging messages (see
+\fBzfs_dbgmsg_enable\fR) for all zios, rather than only for leaf
+zios possessing a vdev. This is meant to be used by developers to gain
+diagnostic information for hang conditions which don't involve a mutex
+or other locking primitive; typically conditions in which a thread in
+the zio pipeline is looping indefinitely.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzio_decompress_fail_fraction\fR (int)
+.ad
+.RS 12n
+If non-zero, this value represents the denominator of the probability that zfs
+should induce a decompression failure. For instance, for a 5% decompression
+failure rate, this value should be set to 20.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzio_slow_io_ms\fR (int)
+.ad
+.RS 12n
+When an I/O operation takes more than \fBzio_slow_io_ms\fR milliseconds to
+complete is marked as a slow I/O. Each slow I/O causes a delay zevent. Slow
+I/O counters can be seen with "zpool status -s".
+
.sp
Default value: \fB30,000\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzio_dva_throttle_enabled\fR (int)
+.ad
+.RS 12n
+Throttle block allocations in the I/O pipeline. This allows for
+dynamic allocation distribution when devices are imbalanced.
+When enabled, the maximum number of pending allocations per top-level vdev
+is limited by \fBzfs_vdev_queue_depth_pct\fR.
+.sp
+Default value: \fB1\fR.
+.RE
+
.sp
.ne 2
.na
.ad
.RS 12n
Percentage of online CPUs (or CPU cores, etc) which will run a worker thread
-for IO. These workers are responsible for IO work such as compression and
+for I/O. These workers are responsible for I/O work such as compression and
checksum calculations. Fractional number of CPUs will be rounded down.
.sp
The default value of 75 was chosen to avoid using all CPUs which can result in
\fBzvol_inhibit_dev\fR (uint)
.ad
.RS 12n
-Do not create zvol device nodes
+Do not create zvol device nodes. This may slightly improve startup time on
+systems with a very large number of zvols.
.sp
Use \fB1\fR for yes and \fB0\fR for no (default).
.RE
\fBzvol_major\fR (uint)
.ad
.RS 12n
-Major number for zvol device
+Major number for zvol block devices
.sp
Default value: \fB230\fR.
.RE
\fBzvol_max_discard_blocks\fR (ulong)
.ad
.RS 12n
-Max number of blocks to discard at once
+Discard (aka TRIM) operations done on zvols will be done in batches of this
+many blocks, where block size is determined by the \fBvolblocksize\fR property
+of a zvol.
.sp
Default value: \fB16,384\fR.
.RE
Default value: \fB131,072\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzvol_request_sync\fR (uint)
+.ad
+.RS 12n
+When processing I/O requests for a zvol submit them synchronously. This
+effectively limits the queue depth to 1 for each I/O submitter. When set
+to 0 requests are handled asynchronously by a thread pool. The number of
+requests which can be handled concurrently is controller by \fBzvol_threads\fR.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzvol_threads\fR (uint)
+.ad
+.RS 12n
+Max number of threads which can handle zvol I/O requests concurrently.
+.sp
+Default value: \fB32\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzvol_volmode\fR (uint)
+.ad
+.RS 12n
+Defines zvol block devices behaviour when \fBvolmode\fR is set to \fBdefault\fR.
+Valid values are \fB1\fR (full), \fB2\fR (dev) and \fB3\fR (none).
+.sp
+Default value: \fB1\fR.
+.RE
+
.SH ZFS I/O SCHEDULER
ZFS issues I/O operations to leaf vdevs to satisfy and complete I/Os.
The I/O scheduler determines when and in what order those operations are
projects / mirror_zfs.git / blobdiff