6146e17ebe
Bold and Normal codes were mixed up in a few places resulting in bad highlighting. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: DHE <git@dehacked.net> Closes #5397
2131 lines
51 KiB
Groff
2131 lines
51 KiB
Groff
'\" te
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.\" Copyright (c) 2013 by Turbo Fredriksson <turbo@bayour.com>. All rights reserved.
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.\" The contents of this file are subject to the terms of the Common Development
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.\" and Distribution License (the "License"). You may not use this file except
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.\" in compliance with the License. You can obtain a copy of the license at
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.\" usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.
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.\"
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.\" See the License for the specific language governing permissions and
|
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.\" limitations under the License. When distributing Covered Code, include this
|
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.\" CDDL HEADER in each file and include the License file at
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.\" usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this
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.\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your
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.\" own identifying information:
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.\" Portions Copyright [yyyy] [name of copyright owner]
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.TH ZFS-MODULE-PARAMETERS 5 "Nov 16, 2013"
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|
.SH NAME
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|
zfs\-module\-parameters \- ZFS module parameters
|
|
.SH DESCRIPTION
|
|
.sp
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|
.LP
|
|
Description of the different parameters to the ZFS module.
|
|
|
|
.SS "Module parameters"
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|
.sp
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|
.LP
|
|
|
|
.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
|
|
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_feed_secs\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
Seconds between L2ARC writing
|
|
.sp
|
|
Default value: \fB1\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBl2arc_headroom\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
How far through the ARC lists to search for L2ARC cacheable content, expressed
|
|
as a multiplier of \fBl2arc_write_max\fR
|
|
.sp
|
|
Default value: \fB2\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
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|
\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
|
|
.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).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBl2arc_noprefetch\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBl2arc_norw\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
No reads during writes
|
|
.sp
|
|
Use \fB1\fR for yes and \fB0\fR for no (default).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBl2arc_write_boost\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
Cold L2ARC devices will have \fBl2arc_write_nax\fR increased by this amount
|
|
while they remain cold.
|
|
.sp
|
|
Default value: \fB8,388,608\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBl2arc_write_max\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
Max write bytes per interval
|
|
.sp
|
|
Default value: \fB8,388,608\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBmetaslab_aliquot\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
Metaslab granularity, in bytes. This is roughly similar to what would be
|
|
referred to as the "stripe size" in traditional RAID arrays. In normal
|
|
operation, ZFS will try to write this amount of data to a top-level vdev
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|
before moving on to the next one.
|
|
.sp
|
|
Default value: \fB524,288\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBmetaslab_bias_enabled\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Enable metaslab group biasing based on its vdev's over- or under-utilization
|
|
relative to the pool.
|
|
.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR for no.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBmetaslab_debug_load\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Load all metaslabs during pool import.
|
|
.sp
|
|
Use \fB1\fR for yes and \fB0\fR for no (default).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBmetaslab_debug_unload\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Prevent metaslabs from being unloaded.
|
|
.sp
|
|
Use \fB1\fR for yes and \fB0\fR for no (default).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBmetaslab_fragmentation_factor_enabled\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Enable use of the fragmentation metric in computing metaslab weights.
|
|
.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR for no.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBmetaslabs_per_vdev\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
When a vdev is added, it will be divided into approximately (but no more than) this number of metaslabs.
|
|
.sp
|
|
Default value: \fB200\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBmetaslab_preload_enabled\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Enable metaslab group preloading.
|
|
.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR for no.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBmetaslab_lba_weighting_enabled\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Give more weight to metaslabs with lower LBAs, assuming they have
|
|
greater bandwidth as is typically the case on a modern constant
|
|
angular velocity disk drive.
|
|
.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR for no.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBspa_config_path\fR (charp)
|
|
.ad
|
|
.RS 12n
|
|
SPA config file
|
|
.sp
|
|
Default value: \fB/etc/zfs/zpool.cache\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBspa_asize_inflation\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Multiplication factor used to estimate actual disk consumption from the
|
|
size of data being written. The default value is a worst case estimate,
|
|
but lower values may be valid for a given pool depending on its
|
|
configuration. Pool administrators who understand the factors involved
|
|
may wish to specify a more realistic inflation factor, particularly if
|
|
they operate close to quota or capacity limits.
|
|
.sp
|
|
Default value: \fB24\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBspa_load_verify_data\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Whether to traverse data blocks during an "extreme rewind" (\fB-X\fR)
|
|
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 0,
|
|
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: \fB1\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBspa_load_verify_metadata\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Whether to traverse blocks during an "extreme rewind" (\fB-X\fR)
|
|
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 0,
|
|
the traversal is not performed. It can be toggled once the import has
|
|
started to stop or start the traversal.
|
|
.sp
|
|
Default value: \fB1\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBspa_load_verify_maxinflight\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Maximum concurrent I/Os during the traversal performed during an "extreme
|
|
rewind" (\fB-X\fR) pool import.
|
|
.sp
|
|
Default value: \fB10000\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBspa_slop_shift\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Normally, we don't allow the last 3.2% (1/(2^spa_slop_shift)) of space
|
|
in the pool to be consumed. This ensures that we don't run the pool
|
|
completely out of space, due to unaccounted changes (e.g. to the MOS).
|
|
It also limits the worst-case time to allocate space. If we have
|
|
less than this amount of free space, most ZPL operations (e.g. write,
|
|
create) will return ENOSPC.
|
|
.sp
|
|
Default value: \fB5\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfetch_array_rd_sz\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
If prefetching is enabled, disable prefetching for reads larger than this size.
|
|
.sp
|
|
Default value: \fB1,048,576\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfetch_max_distance\fR (uint)
|
|
.ad
|
|
.RS 12n
|
|
Max bytes to prefetch per stream (default 8MB).
|
|
.sp
|
|
Default value: \fB8,388,608\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfetch_max_streams\fR (uint)
|
|
.ad
|
|
.RS 12n
|
|
Max number of streams per zfetch (prefetch streams per file).
|
|
.sp
|
|
Default value: \fB8\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfetch_min_sec_reap\fR (uint)
|
|
.ad
|
|
.RS 12n
|
|
Min time before an active prefetch stream can be reclaimed
|
|
.sp
|
|
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 floor 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% of the number of dnodes in the ARC\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_average_blocksize\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
The ARC's buffer hash table is sized based on the assumption of an average
|
|
block size of \fBzfs_arc_average_blocksize\fR (default 8K). This works out
|
|
to roughly 1MB of hash table per 1GB of physical memory with 8-byte pointers.
|
|
For configurations with a known larger average block size this value can be
|
|
increased to reduce the memory footprint.
|
|
|
|
.sp
|
|
Default value: \fB8192\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_evict_batch_limit\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Number ARC headers to evict per sub-list before proceeding to another sub-list.
|
|
This batch-style operation prevents entire sub-lists from being evicted at once
|
|
but comes at a cost of additional unlocking and locking.
|
|
.sp
|
|
Default value: \fB10\fR.
|
|
.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
|
|
.sp
|
|
Default value: \fB5\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_lotsfree_percent\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_max\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
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_limit\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
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 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
|
|
\fBzfs_arc_meta_min\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
The minimum allowed size in bytes that meta data buffers may consume in
|
|
the ARC. This value defaults to 0 which disables a floor on the amount
|
|
of the ARC devoted meta data.
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_meta_prune\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
The number of dentries and inodes to be scanned looking for entries
|
|
which can be dropped. This may be required when the ARC reaches the
|
|
\fBzfs_arc_meta_limit\fR because dentries and inodes can pin buffers
|
|
in the ARC. Increasing this value will cause to dentry and inode caches
|
|
to be pruned more aggressively. Setting this value to 0 will disable
|
|
pruning the inode and dentry caches.
|
|
.sp
|
|
Default value: \fB10,000\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
|
|
\fBzfs_arc_min\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
Min arc size
|
|
.sp
|
|
Default value: \fB100\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_min_prefetch_lifespan\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.
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_num_sublists_per_state\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.
|
|
.sp
|
|
Default value: \fB1\fR or the number of online CPUs, whichever is greater
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_overflow_shift\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
The ARC size is considered to be overflowing if it exceeds the current
|
|
ARC target size (arc_c) by a threshold determined by this parameter.
|
|
The threshold is calculated as a fraction of arc_c using the formula
|
|
"arc_c >> \fBzfs_arc_overflow_shift\fR".
|
|
|
|
The default value of 8 causes the ARC to be considered to be overflowing
|
|
if it exceeds the target size by 1/256th (0.3%) of the target size.
|
|
|
|
When the ARC is overflowing, new buffer allocations are stalled until
|
|
the reclaim thread catches up and the overflow condition no longer exists.
|
|
.sp
|
|
Default value: \fB8\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
|
|
\fBzfs_arc_p_min_shift\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
arc_c shift to calc min/max arc_p
|
|
.sp
|
|
Default value: \fB4\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_p_aggressive_disable\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Disable aggressive arc_p growth
|
|
.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR to disable.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_p_dampener_disable\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Disable arc_p adapt dampener
|
|
.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR to disable.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_shrink_shift\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
log2(fraction of arc to reclaim)
|
|
.sp
|
|
Default value: \fB5\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_arc_sys_free\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
The target number of bytes the ARC should leave as free memory on the system.
|
|
Defaults to the larger of 1/64 of physical memory or 512K. Setting this
|
|
option to a non-zero value will override the default.
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_autoimport_disable\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Disable pool import at module load by ignoring the cache file (typically \fB/etc/zfs/zpool.cache\fR).
|
|
.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR for no.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_dbgmsg_enable\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.
|
|
.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
|
|
Enable deadman timer. See description below.
|
|
.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR to disable.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\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.
|
|
.sp
|
|
Default value: \fB1,000,000\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
|
|
.na
|
|
\fBzfs_delay_min_dirty_percent\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Start to delay each transaction once there is this amount of dirty data,
|
|
expressed as a percentage of \fBzfs_dirty_data_max\fR.
|
|
This value should be >= zfs_vdev_async_write_active_max_dirty_percent.
|
|
See the section "ZFS TRANSACTION DELAY".
|
|
.sp
|
|
Default value: \fB60\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_delay_scale\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
This controls how quickly the transaction delay approaches infinity.
|
|
Larger values cause longer delays for a given amount of dirty data.
|
|
.sp
|
|
For the smoothest delay, this value should be about 1 billion divided
|
|
by the maximum number of operations per second. This will smoothly
|
|
handle between 10x and 1/10th this number.
|
|
.sp
|
|
See the section "ZFS TRANSACTION DELAY".
|
|
.sp
|
|
Note: \fBzfs_delay_scale\fR * \fBzfs_dirty_data_max\fR must be < 2^64.
|
|
.sp
|
|
Default value: \fB500,000\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_delete_blocks\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
This is the used to define a large file for the purposes of delete. Files
|
|
containing more than \fBzfs_delete_blocks\fR will be deleted asynchronously
|
|
while smaller files are deleted synchronously. Decreasing this value will
|
|
reduce the time spent in an unlink(2) system call at the expense of a longer
|
|
delay before the freed space is available.
|
|
.sp
|
|
Default value: \fB20,480\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_dirty_data_max\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Determines the dirty space limit in bytes. Once this limit is exceeded, new
|
|
writes are halted until space frees up. This parameter takes precedence
|
|
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.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_dirty_data_max_max\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Maximum allowable value of \fBzfs_dirty_data_max\fR, expressed in bytes.
|
|
This limit is only enforced at module load time, and will be ignored if
|
|
\fBzfs_dirty_data_max\fR is later changed. This parameter takes
|
|
precedence over \fBzfs_dirty_data_max_max_percent\fR. See the section
|
|
"ZFS TRANSACTION DELAY".
|
|
.sp
|
|
Default value: 25% of physical RAM.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_dirty_data_max_max_percent\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Maximum allowable value of \fBzfs_dirty_data_max\fR, expressed as a
|
|
percentage of physical RAM. This limit is only enforced at module load
|
|
time, and will be ignored if \fBzfs_dirty_data_max\fR is later changed.
|
|
The parameter \fBzfs_dirty_data_max_max\fR takes precedence over this
|
|
one. See the section "ZFS TRANSACTION DELAY".
|
|
.sp
|
|
Default value: \fN25\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_dirty_data_max_percent\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Determines the dirty space limit, expressed as a percentage of all
|
|
memory. Once this limit is exceeded, new writes are halted until space frees
|
|
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.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_dirty_data_sync\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Start syncing out a transaction group if there is at least this much dirty data.
|
|
.sp
|
|
Default value: \fB67,108,864\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_fletcher_4_impl\fR (string)
|
|
.ad
|
|
.RS 12n
|
|
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: \fBfastest\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_free_bpobj_enabled\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Enable/disable the processing of the free_bpobj object.
|
|
.sp
|
|
Default value: \fB1\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_free_max_blocks\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
Maximum number of blocks freed in a single txg.
|
|
.sp
|
|
Default value: \fB100,000\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_async_read_max_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Maximum asynchronous read I/Os active to each device.
|
|
See the section "ZFS I/O SCHEDULER".
|
|
.sp
|
|
Default value: \fB3\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_async_read_min_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Minimum asynchronous read 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_async_write_active_max_dirty_percent\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
When the pool has more than
|
|
\fBzfs_vdev_async_write_active_max_dirty_percent\fR dirty data, use
|
|
\fBzfs_vdev_async_write_max_active\fR to limit active async writes. If
|
|
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.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_async_write_active_min_dirty_percent\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
When the pool has less than
|
|
\fBzfs_vdev_async_write_active_min_dirty_percent\fR dirty data, use
|
|
\fBzfs_vdev_async_write_min_active\fR to limit active async writes. If
|
|
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.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_async_write_max_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Maximum asynchronous write I/Os active to each device.
|
|
See the section "ZFS I/O SCHEDULER".
|
|
.sp
|
|
Default value: \fB10\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_async_write_min_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Minimum asynchronous write 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_max_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
The maximum number of I/Os active to each device. Ideally, this will be >=
|
|
the sum of each queue's max_active. It must be at least the sum of each
|
|
queue's min_active. See the section "ZFS I/O SCHEDULER".
|
|
.sp
|
|
Default value: \fB1,000\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_scrub_max_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Maximum scrub 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_scrub_min_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Minimum scrub 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_sync_read_max_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Maximum synchronous read I/Os active to each device.
|
|
See the section "ZFS I/O SCHEDULER".
|
|
.sp
|
|
Default value: \fB10\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_sync_read_min_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Minimum synchronous read I/Os active to each device.
|
|
See the section "ZFS I/O SCHEDULER".
|
|
.sp
|
|
Default value: \fB10\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_sync_write_max_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Maximum synchronous write I/Os active to each device.
|
|
See the section "ZFS I/O SCHEDULER".
|
|
.sp
|
|
Default value: \fB10\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_sync_write_min_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Minimum synchronous write I/Os active to each device.
|
|
See the section "ZFS I/O SCHEDULER".
|
|
.sp
|
|
Default value: \fB10\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_queue_depth_pct\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
The queue depth percentage for each top-level virtual device.
|
|
Used in conjunction with zfs_vdev_async_max_active.
|
|
.sp
|
|
Default value: \fB1000\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_disable_dup_eviction\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Disable duplicate buffer eviction
|
|
.sp
|
|
Use \fB1\fR for yes and \fB0\fR for no (default).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_expire_snapshot\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Seconds to expire .zfs/snapshot
|
|
.sp
|
|
Default value: \fB300\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_admin_snapshot\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Allow the creation, removal, or renaming of entries in the .zfs/snapshot
|
|
directory to cause the creation, destruction, or renaming of snapshots.
|
|
When enabled this functionality works both locally and over NFS exports
|
|
which have the 'no_root_squash' option set. This functionality is disabled
|
|
by default.
|
|
.sp
|
|
Use \fB1\fR for yes and \fB0\fR for no (default).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_flags\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Set additional debugging flags. The following flags may be bitwise-or'd
|
|
together.
|
|
.sp
|
|
.TS
|
|
box;
|
|
rB lB
|
|
lB lB
|
|
r l.
|
|
Value Symbolic Name
|
|
Description
|
|
_
|
|
1 ZFS_DEBUG_DPRINTF
|
|
Enable dprintf entries in the debug log.
|
|
_
|
|
2 ZFS_DEBUG_DBUF_VERIFY *
|
|
Enable extra dbuf verifications.
|
|
_
|
|
4 ZFS_DEBUG_DNODE_VERIFY *
|
|
Enable extra dnode verifications.
|
|
_
|
|
8 ZFS_DEBUG_SNAPNAMES
|
|
Enable snapshot name verification.
|
|
_
|
|
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.
|
|
.TE
|
|
.sp
|
|
* Requires debug build.
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_free_leak_on_eio\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
If destroy encounters an EIO while reading metadata (e.g. indirect
|
|
blocks), space referenced by the missing metadata can not be freed.
|
|
Normally this causes the background destroy to become "stalled", as
|
|
it is unable to make forward progress. While in this stalled state,
|
|
all remaining space to free from the error-encountering filesystem is
|
|
"temporarily leaked". Set this flag to cause it to ignore the EIO,
|
|
permanently leak the space from indirect blocks that can not be read,
|
|
and continue to free everything else that it can.
|
|
|
|
The default, "stalling" behavior is useful if the storage partially
|
|
fails (i.e. some but not all i/os fail), and then later recovers. In
|
|
this case, we will be able to continue pool operations while it is
|
|
partially failed, and when it recovers, we can continue to free the
|
|
space, with no leaks. However, note that this case is actually
|
|
fairly rare.
|
|
|
|
Typically pools either (a) fail completely (but perhaps temporarily,
|
|
e.g. a top-level vdev going offline), or (b) have localized,
|
|
permanent errors (e.g. disk returns the wrong data due to bit flip or
|
|
firmware bug). In case (a), this setting does not matter because the
|
|
pool will be suspended and the sync thread will not be able to make
|
|
forward progress regardless. In case (b), because the error is
|
|
permanent, the best we can do is leak the minimum amount of space,
|
|
which is what setting this flag will do. Therefore, it is reasonable
|
|
for this flag to normally be set, but we chose the more conservative
|
|
approach of not setting it, so that there is no possibility of
|
|
leaking space in the "partial temporary" failure case.
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_free_min_time_ms\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_immediate_write_sz\fR (long)
|
|
.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 \fBlogbias=throughput\fR.
|
|
.sp
|
|
Default value: \fB32,768\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_max_recordsize\fR (int)
|
|
.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
|
|
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
|
|
zfs_max_recordsize (default 1MB). Larger blocks can be created by changing
|
|
this tunable, and pools with larger blocks can always be imported and used,
|
|
regardless of this setting.
|
|
.sp
|
|
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
|
|
\fBzfs_metaslab_fragmentation_threshold\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Allow metaslabs to keep their active state as long as their fragmentation
|
|
percentage is less than or equal to this value. An active metaslab that
|
|
exceeds this threshold will no longer keep its active status allowing
|
|
better metaslabs to be selected.
|
|
.sp
|
|
Default value: \fB70\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_mg_fragmentation_threshold\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Metaslab groups are considered eligible for allocations if their
|
|
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.
|
|
.sp
|
|
Default value: \fB85\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_mg_noalloc_threshold\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Defines a threshold at which metaslab groups should be eligible for
|
|
allocations. The value is expressed as a percentage of free space
|
|
beyond which a metaslab group is always eligible for allocations.
|
|
If a metaslab group's free space is less than or equal to the
|
|
threshold, the allocator will avoid allocating to that group
|
|
unless all groups in the pool have reached the threshold. Once all
|
|
groups have reached the threshold, all groups are allowed to accept
|
|
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
|
|
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
|
|
and allow lesser filled vdevs to acquire more allocations than they
|
|
otherwise would under the old \fBzfs_mg_alloc_failures\fR facility.
|
|
.sp
|
|
Default value: \fB0\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. Beware, this may cause
|
|
corruption if disks re-order writes.
|
|
.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_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_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_read_chunk_size\fR (long)
|
|
.ad
|
|
.RS 12n
|
|
Bytes to read per chunk
|
|
.sp
|
|
Default value: \fB1,048,576\fR.
|
|
.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
|
|
.sp
|
|
Default value: \fB0\fR (no data is kept).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_read_history_hits\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Include cache hits in read history
|
|
.sp
|
|
Use \fB1\fR for yes and \fB0\fR for no (default).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_recover\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.
|
|
.sp
|
|
Use \fB1\fR for yes and \fB0\fR for no (default).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_resilver_delay\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.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_resilver_min_time_ms\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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)
|
|
.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.
|
|
.sp
|
|
Default value: \fB50\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_scan_min_time_ms\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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)
|
|
.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.
|
|
.sp
|
|
Default value: \fB4\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_send_corrupt_data\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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_sync_pass_deferred_free\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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_sync_pass_dont_compress\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Don't compress starting in this pass
|
|
.sp
|
|
Default value: \fB5\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_sync_pass_rewrite\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Rewrite new block pointers starting in this pass
|
|
.sp
|
|
Default value: \fB2\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_top_maxinflight\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Max concurrent I/Os per top-level vdev (mirrors or raidz arrays) allowed during
|
|
scrub or resilver operations.
|
|
.sp
|
|
Default value: \fB32\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\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
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_txg_timeout\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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_aggregation_limit\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Max vdev I/O aggregation size
|
|
.sp
|
|
Default value: \fB131,072\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_cache_bshift\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Shift size to inflate reads too
|
|
.sp
|
|
Default value: \fB16\fR (effectively 65536).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_cache_max\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Inflate reads small than this value to meet the \fBzfs_vdev_cache_bshift\fR
|
|
size.
|
|
.sp
|
|
Default value: \fB16384\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_cache_size\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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_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 when an I/O immediately
|
|
follows its predecessor on rotational vdevs for the purpose of making decisions
|
|
based on load.
|
|
.sp
|
|
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
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_read_gap_limit\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Aggregate read I/O operations if the gap on-disk between them is within this
|
|
threshold.
|
|
.sp
|
|
Default value: \fB32,768\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_scheduler\fR (charp)
|
|
.ad
|
|
.RS 12n
|
|
Set the Linux I/O scheduler on whole disk vdevs to this scheduler
|
|
.sp
|
|
Default value: \fBnoop\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_write_gap_limit\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Aggregate write I/O over gap
|
|
.sp
|
|
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
|
|
When zevents are logged to the console use this as the word wrap width.
|
|
.sp
|
|
Default value: \fB80\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_zevent_console\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Log events to the console
|
|
.sp
|
|
Use \fB1\fR for yes and \fB0\fR for no (default).
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_zevent_len_max\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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
|
|
\fBzil_replay_disable\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
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)
|
|
.ad
|
|
.RS 12n
|
|
Max commit bytes to separate log device
|
|
.sp
|
|
Default value: \fB1,048,576\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzio_delay_max\fR (int)
|
|
.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
|
|
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.
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzio_requeue_io_start_cut_in_line\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Prioritize requeued I/O
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzio_taskq_batch_pct\fR (uint)
|
|
.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
|
|
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
|
|
latency issues and inconsistent application performance, especially when high
|
|
compression is enabled.
|
|
.sp
|
|
Default value: \fB75\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzvol_inhibit_dev\fR (uint)
|
|
.ad
|
|
.RS 12n
|
|
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
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzvol_major\fR (uint)
|
|
.ad
|
|
.RS 12n
|
|
Major number for zvol block devices
|
|
.sp
|
|
Default value: \fB230\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzvol_max_discard_blocks\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
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
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzvol_prefetch_bytes\fR (uint)
|
|
.ad
|
|
.RS 12n
|
|
When adding a zvol to the system prefetch \fBzvol_prefetch_bytes\fR
|
|
from the start and end of the volume. Prefetching these regions
|
|
of the volume is desirable because they are likely to be accessed
|
|
immediately by \fBblkid(8)\fR or by the kernel scanning for a partition
|
|
table.
|
|
.sp
|
|
Default value: \fB131,072\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
|
|
issued. The I/O scheduler divides operations into five I/O classes
|
|
prioritized in the following order: sync read, sync write, async read,
|
|
async write, and scrub/resilver. Each queue defines the minimum and
|
|
maximum number of concurrent operations that may be issued to the
|
|
device. In addition, the device has an aggregate maximum,
|
|
\fBzfs_vdev_max_active\fR. Note that the sum of the per-queue minimums
|
|
must not exceed the aggregate maximum. If the sum of the per-queue
|
|
maximums exceeds the aggregate maximum, then the number of active I/Os
|
|
may reach \fBzfs_vdev_max_active\fR, in which case no further I/Os will
|
|
be issued regardless of whether all per-queue minimums have been met.
|
|
.sp
|
|
For many physical devices, throughput increases with the number of
|
|
concurrent operations, but latency typically suffers. Further, physical
|
|
devices typically have a limit at which more concurrent operations have no
|
|
effect on throughput or can actually cause it to decrease.
|
|
.sp
|
|
The scheduler selects the next operation to issue by first looking for an
|
|
I/O class whose minimum has not been satisfied. Once all are satisfied and
|
|
the aggregate maximum has not been hit, the scheduler looks for classes
|
|
whose maximum has not been satisfied. Iteration through the I/O classes is
|
|
done in the order specified above. No further operations are issued if the
|
|
aggregate maximum number of concurrent operations has been hit or if there
|
|
are no operations queued for an I/O class that has not hit its maximum.
|
|
Every time an I/O is queued or an operation completes, the I/O scheduler
|
|
looks for new operations to issue.
|
|
.sp
|
|
In general, smaller max_active's will lead to lower latency of synchronous
|
|
operations. Larger max_active's may lead to higher overall throughput,
|
|
depending on underlying storage.
|
|
.sp
|
|
The ratio of the queues' max_actives determines the balance of performance
|
|
between reads, writes, and scrubs. E.g., increasing
|
|
\fBzfs_vdev_scrub_max_active\fR will cause the scrub or resilver to complete
|
|
more quickly, but reads and writes to have higher latency and lower throughput.
|
|
.sp
|
|
All I/O classes have a fixed maximum number of outstanding operations
|
|
except for the async write class. Asynchronous writes represent the data
|
|
that is committed to stable storage during the syncing stage for
|
|
transaction groups. Transaction groups enter the syncing state
|
|
periodically so the number of queued async writes will quickly burst up
|
|
and then bleed down to zero. Rather than servicing them as quickly as
|
|
possible, the I/O scheduler changes the maximum number of active async
|
|
write I/Os according to the amount of dirty data in the pool. Since
|
|
both throughput and latency typically increase with the number of
|
|
concurrent operations issued to physical devices, reducing the
|
|
burstiness in the number of concurrent operations also stabilizes the
|
|
response time of operations from other -- and in particular synchronous
|
|
-- queues. In broad strokes, the I/O scheduler will issue more
|
|
concurrent operations from the async write queue as there's more dirty
|
|
data in the pool.
|
|
.sp
|
|
Async Writes
|
|
.sp
|
|
The number of concurrent operations issued for the async write I/O class
|
|
follows a piece-wise linear function defined by a few adjustable points.
|
|
.nf
|
|
|
|
| o---------| <-- zfs_vdev_async_write_max_active
|
|
^ | /^ |
|
|
| | / | |
|
|
active | / | |
|
|
I/O | / | |
|
|
count | / | |
|
|
| / | |
|
|
|-------o | | <-- zfs_vdev_async_write_min_active
|
|
0|_______^______|_________|
|
|
0% | | 100% of zfs_dirty_data_max
|
|
| |
|
|
| `-- zfs_vdev_async_write_active_max_dirty_percent
|
|
`--------- zfs_vdev_async_write_active_min_dirty_percent
|
|
|
|
.fi
|
|
Until the amount of dirty data exceeds a minimum percentage of the dirty
|
|
data allowed in the pool, the I/O scheduler will limit the number of
|
|
concurrent operations to the minimum. As that threshold is crossed, the
|
|
number of concurrent operations issued increases linearly to the maximum at
|
|
the specified maximum percentage of the dirty data allowed in the pool.
|
|
.sp
|
|
Ideally, the amount of dirty data on a busy pool will stay in the sloped
|
|
part of the function between \fBzfs_vdev_async_write_active_min_dirty_percent\fR
|
|
and \fBzfs_vdev_async_write_active_max_dirty_percent\fR. If it exceeds the
|
|
maximum percentage, this indicates that the rate of incoming data is
|
|
greater than the rate that the backend storage can handle. In this case, we
|
|
must further throttle incoming writes, as described in the next section.
|
|
|
|
.SH ZFS TRANSACTION DELAY
|
|
We delay transactions when we've determined that the backend storage
|
|
isn't able to accommodate the rate of incoming writes.
|
|
.sp
|
|
If there is already a transaction waiting, we delay relative to when
|
|
that transaction will finish waiting. This way the calculated delay time
|
|
is independent of the number of threads concurrently executing
|
|
transactions.
|
|
.sp
|
|
If we are the only waiter, wait relative to when the transaction
|
|
started, rather than the current time. This credits the transaction for
|
|
"time already served", e.g. reading indirect blocks.
|
|
.sp
|
|
The minimum time for a transaction to take is calculated as:
|
|
.nf
|
|
min_time = zfs_delay_scale * (dirty - min) / (max - dirty)
|
|
min_time is then capped at 100 milliseconds.
|
|
.fi
|
|
.sp
|
|
The delay has two degrees of freedom that can be adjusted via tunables. The
|
|
percentage of dirty data at which we start to delay is defined by
|
|
\fBzfs_delay_min_dirty_percent\fR. This should typically be at or above
|
|
\fBzfs_vdev_async_write_active_max_dirty_percent\fR so that we only start to
|
|
delay after writing at full speed has failed to keep up with the incoming write
|
|
rate. The scale of the curve is defined by \fBzfs_delay_scale\fR. Roughly speaking,
|
|
this variable determines the amount of delay at the midpoint of the curve.
|
|
.sp
|
|
.nf
|
|
delay
|
|
10ms +-------------------------------------------------------------*+
|
|
| *|
|
|
9ms + *+
|
|
| *|
|
|
8ms + *+
|
|
| * |
|
|
7ms + * +
|
|
| * |
|
|
6ms + * +
|
|
| * |
|
|
5ms + * +
|
|
| * |
|
|
4ms + * +
|
|
| * |
|
|
3ms + * +
|
|
| * |
|
|
2ms + (midpoint) * +
|
|
| | ** |
|
|
1ms + v *** +
|
|
| zfs_delay_scale ----------> ******** |
|
|
0 +-------------------------------------*********----------------+
|
|
0% <- zfs_dirty_data_max -> 100%
|
|
.fi
|
|
.sp
|
|
Note that since the delay is added to the outstanding time remaining on the
|
|
most recent transaction, the delay is effectively the inverse of IOPS.
|
|
Here the midpoint of 500us translates to 2000 IOPS. The shape of the curve
|
|
was chosen such that small changes in the amount of accumulated dirty data
|
|
in the first 3/4 of the curve yield relatively small differences in the
|
|
amount of delay.
|
|
.sp
|
|
The effects can be easier to understand when the amount of delay is
|
|
represented on a log scale:
|
|
.sp
|
|
.nf
|
|
delay
|
|
100ms +-------------------------------------------------------------++
|
|
+ +
|
|
| |
|
|
+ *+
|
|
10ms + *+
|
|
+ ** +
|
|
| (midpoint) ** |
|
|
+ | ** +
|
|
1ms + v **** +
|
|
+ zfs_delay_scale ----------> ***** +
|
|
| **** |
|
|
+ **** +
|
|
100us + ** +
|
|
+ * +
|
|
| * |
|
|
+ * +
|
|
10us + * +
|
|
+ +
|
|
| |
|
|
+ +
|
|
+--------------------------------------------------------------+
|
|
0% <- zfs_dirty_data_max -> 100%
|
|
.fi
|
|
.sp
|
|
Note here that only as the amount of dirty data approaches its limit does
|
|
the delay start to increase rapidly. The goal of a properly tuned system
|
|
should be to keep the amount of dirty data out of that range by first
|
|
ensuring that the appropriate limits are set for the I/O scheduler to reach
|
|
optimal throughput on the backend storage, and then by changing the value
|
|
of \fBzfs_delay_scale\fR to increase the steepness of the curve.
|