'\" te
.\" Copyright (c) 2013 by Turbo Fredriksson <turbo@bayour.com>. All rights reserved.
+.\" Copyright (c) 2017 Datto Inc.
+.\" Copyright (c) 2018 by Delphix. All rights reserved.
.\" 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 "Oct 28, 2017"
.SH NAME
zfs\-module\-parameters \- ZFS module parameters
.SH DESCRIPTION
.sp
.LP
+.sp
+.ne 2
+.na
+\fBdbuf_cache_max_bytes\fR (ulong)
+.ad
+.RS 12n
+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
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBdbuf_cache_hiwater_pct\fR (uint)
+.ad
+.RS 12n
+The percentage over \fBdbuf_cache_max_bytes\fR when dbufs must be evicted
+directly.
+.sp
+Default value: \fB10\fR%.
+.RE
+
+.sp
+.ne 2
+.na
+\fBdbuf_cache_lowater_pct\fR (uint)
+.ad
+.RS 12n
+The percentage below \fBdbuf_cache_max_bytes\fR when the evict thread stops
+evicting dbufs.
+.sp
+Default value: \fB10\fR%.
+.RE
+
+.sp
+.ne 2
+.na
+\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
+\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
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
-.ne 2
-.na
-\fBl2arc_max_block_size\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.
-.sp
-Default value: \fB16,777,216\fR.
-.RE
-
-.sp
-.ne 2
-.na
-\fBl2arc_nocompress\fR (int)
-.ad
-.RS 12n
-Skip compressing L2ARC buffers
-.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
+Default value: \fB200\fR%.
.RE
.sp
\fBl2arc_write_boost\fR (ulong)
.ad
.RS 12n
-Cold L2ARC devices will have \fBl2arc_write_nax\fR increased by this amount
+Cold L2ARC devices will have \fBl2arc_write_max\fR increased by this amount
while they remain cold.
.sp
Default value: \fB8,388,608\fR.
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
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
.ne 2
.na
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
.ne 2
.na
Default value: \fB2\fR.
.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
-After a memory pressure event the ARC will wait this many seconds before trying
-to resume growth
+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
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 3/4 of the ARC; it must be set to an explicit value.
+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: \fB100\fR.
+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_prefetch_lifespan\fR (int)
+\fBzfs_arc_min_prescient_prefetch_ms\fR (int)
.ad
.RS 12n
-Minimum time prefetched blocks are locked in the ARC, specified in jiffies.
-A value of 0 will default to 1 second.
+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: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_arc_num_sublists_per_state\fR (int)
+\fBzfs_max_missing_tvds\fR (int)
+.ad
+.RS 12n
+Number of missing top-level vdevs which will be allowed during
+pool import (only in read-only mode).
+.sp
+Default value: \fB0\fR
+.RE
+
+.sp
+.ne 2
+.na
+\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: \fR1\fB or the number of 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
Use \fB1\fR for yes (default) and \fB0\fR for no.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_checksums_per_second\fR (int)
+.ad
+.RS 12n
+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: 20
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_commit_timeout_pct\fR (int)
+.ad
+.RS 12n
+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: \fB5\fR%.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_condense_indirect_vdevs_enable\fR (int)
+.ad
+.RS 12n
+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: \fB1\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_condense_max_obsolete_bytes\fR (ulong)
+.ad
+.RS 12n
+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
+Default value: \fB1,073,741,824\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_condense_min_mapping_bytes\fR (ulong)
+.ad
+.RS 12n
+Minimum size vdev mapping to attempt to condense (see
+\fBzfs_condense_indirect_vdevs_enable\fR).
+.sp
+Default value: \fB131,072\fR.
+.RE
+
.sp
.ne 2
.na
\fBzfs_deadman_enabled\fR (int)
.ad
.RS 12n
-Enable deadman timer. See description below.
+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
-Use \fB1\fR for yes (default) and \fB0\fR to disable.
+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
\fBzfs_deadman_synctime_ms\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.
+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 IO 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: \fB1,000,000\fR.
+Default value: \fB300,000\fR.
.RE
.sp
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_delays_per_second\fR (int)
+.ad
+.RS 12n
+Rate limit IO delay events to this many per second.
+.sp
+Default value: 20
+.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: \fN25\fR.
+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
.RS 12n
Select a fletcher 4 implementation.
.sp
-Supported selectors are: \fBfastest\fR, \fBscalar\fR, and \fBavx2\fR when
-AVX2 is supported by the processor. 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, \fBavx2\fR uses the AVX2 vector instructions to compute a fletcher 4.
+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: \fBfastest\fR.
.RE
.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
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
Minimum asynchronous write I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
.sp
-Default value: \fB1\fR.
+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
.sp
.ne 2
.na
-\fBzfs_disable_dup_eviction\fR (int)
+\fBzfs_vdev_queue_depth_pct\fR (int)
.ad
.RS 12n
-Disable duplicate buffer eviction
+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
-Use \fB1\fR for yes and \fB0\fR for no (default).
+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.
.TE
.sp
* Requires debug build.
\fBzfs_free_min_time_ms\fR (int)
.ad
.RS 12n
-During a \fRzfs destroy\fB operation using \fRfeature@async_destroy\fB a minimum
+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.
.ad
.RS 12n
Largest data block to write to zil. Larger blocks will be treated as if the
-dataset being written to had the property setting \fRlogbias=throughput\fB.
+dataset being written to had the property setting \fBlogbias=throughput\fR.
.sp
Default value: \fB32,768\fR.
.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
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
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
Default value: \fB0\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_multihost_history\fR (int)
+.ad
+.RS 12n
+Historical statistics for the last N multihost updates will be available in
+\fB/proc/spl/kstat/zfs/<pool>/multihost\fR
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_multihost_interval\fR (ulong)
+.ad
+.RS 12n
+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
+The multihost write period is \fBzfs_multihost_interval / leaf-vdevs\fR milliseconds.
+This means that 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
+On import the activity check waits a minimum amount of time determined by
+\fBzfs_multihost_interval * zfs_multihost_import_intervals\fR. 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
+Default value: \fB1000\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_multihost_import_intervals\fR (uint)
+.ad
+.RS 12n
+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. A value of 0 is ignored and treated as
+if it was set to 1
+.sp
+Default value: \fB10\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_multihost_fail_intervals\fR (uint)
+.ad
+.RS 12n
+Controls the behavior of the pool when multihost write failures are detected.
+.sp
+When \fBzfs_multihost_fail_intervals = 0\fR then multihost write failures 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
+When \fBzfs_multihost_fail_intervals > 0\fR then sequential multihost write failures
+will cause the pool to be suspended. This occurs when
+\fBzfs_multihost_fail_intervals * zfs_multihost_interval\fR milliseconds have
+passed since the last successful multihost write. This guarantees the activity test
+will see multihost writes if the pool is imported.
+.sp
+Default value: \fB5\fR.
+.RE
+
.sp
.ne 2
.na
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
.ad
.RS 12n
The number of bytes which should be prefetched during a pool traversal
-(eg: \fRzfs send\fB or other data crawling operations)
+(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 blocks from frees in one TXG.
+After this threshold is crossed, additional dirty blocks from frees
+wait until the next TXG.
+A value of zero will disable this throttle.
+.sp
+Default value: \fB30\fR and \fB0\fR to disable.
+.RE
+
+
+
.sp
.ne 2
.na
\fBzfs_read_history\fR (int)
.ad
.RS 12n
-Historic statistics for the last N reads will be available in
-\fR/proc/spl/kstat/zfs/POOLNAME/reads\fB
+Historical statistics for the last N reads will be available in
+\fB/proc/spl/kstat/zfs/<pool>/reads\fR
.sp
Default value: \fB0\fR (no data is kept).
.RE
.sp
.ne 2
.na
-\fBzfs_recover\fR (int)
+\fBzfs_reconstruct_indirect_combinations_max\fR (int)
.ad
-.RS 12n
-Set to attempt to recover from fatal errors. This should only be used as a
-last resort, as it typically results in leaked space, or worse.
+.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
-Use \fB1\fR for yes and \fB0\fR for no (default).
+Default value: \fB100\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_resilver_delay\fR (int)
+\fBzfs_recover\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.
+Set to attempt to recover from fatal errors. This should only be used as a
+last resort, as it typically results in leaked space, or worse.
.sp
-Default value: \fB2\fR.
+Use \fB1\fR for yes and \fB0\fR for no (default).
.RE
.sp
.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
Scrubs are processed by the sync thread. While scrubbing it will spend
.sp
.ne 2
.na
-\fBzfs_scrub_delay\fR (int)
+\fBzfs_scan_checkpoint_intval\fR (int)
+.ad
+.RS 12n
+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
+\fBfBzfs_scan_checkpoint_intval\fR tunable.
+.sp
+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
-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.
+Maximum amount of data that can be concurrently issued at once for scrubs and
+resilvers per leaf device, given in bytes.
.sp
-Default value: \fB4\fR.
+Default value: \fB41943040\fR.
.RE
.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
.sp
.ne 2
.na
-\fBzfs_top_maxinflight\fR (int)
+\fBzfs_sync_taskq_batch_pct\fR (int)
.ad
.RS 12n
-Max concurrent I/Os per top-level vdev (mirrors or raidz arrays) allowed 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: \fB32\fR.
+Default value: \fB75\fR%.
.RE
.sp
\fBzfs_txg_history\fR (int)
.ad
.RS 12n
-Historic statistics for the last N txgs will be available in
-\fR/proc/spl/kstat/zfs/POOLNAME/txgs\fB
+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_vdev_cache_max\fR (int)
.ad
.RS 12n
-Inflate reads small than this value to meet the \fBzfs_vdev_cache_bshift\fR
-size.
+Inflate reads smaller than this value to meet the \fBzfs_vdev_cache_bshift\fR
+size (default 64k).
.sp
Default value: \fB16384\fR.
.RE
\fBzfs_vdev_scheduler\fR (charp)
.ad
.RS 12n
-Set the Linux I/O scheduler on whole disk vdevs to this 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
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
.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
.ad
.RS 12n
A zevent will be logged if a ZIO operation takes more than N milliseconds to
-complete. Note that this is only a logging facility, not a timeout on
+complete. Note that this is only a logging facility, not a timeout on
operations.
.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 ZIO 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
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
+
+.sp
+.ne 2
+.na
+\fBzfs_qat_disable\fR (int)
+.ad
+.RS 12n
+This tunable disables qat hardware acceleration for gzip compression and.
+AES-GCM encryption. It is available only if qat acceleration is compiled in
+and the qat driver is present.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.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