1365 lines
28 KiB
Groff
1365 lines
28 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
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.SH DESCRIPTION
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.sp
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.LP
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Description of the different parameters to the ZFS module.
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.SS "Module parameters"
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.sp
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.LP
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.sp
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.ne 2
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.na
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|
\fBl2arc_feed_again\fR (int)
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|
.ad
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.RS 12n
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|
Turbo L2ARC warmup
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.sp
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Use \fB1\fR for yes (default) and \fB0\fR to disable.
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.RE
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.sp
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.ne 2
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.na
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\fBl2arc_feed_min_ms\fR (ulong)
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.ad
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.RS 12n
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|
Min feed interval in milliseconds
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.sp
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|
Default value: \fB200\fR.
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.RE
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.sp
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.ne 2
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.na
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|
\fBl2arc_feed_secs\fR (ulong)
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|
.ad
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.RS 12n
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|
Seconds between L2ARC writing
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|
.sp
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|
Default value: \fB1\fR.
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.RE
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|
.sp
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.ne 2
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.na
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|
\fBl2arc_headroom\fR (ulong)
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|
.ad
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|
.RS 12n
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|
Number of max device writes to precache
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.sp
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|
Default value: \fB2\fR.
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.RE
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.sp
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.ne 2
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.na
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|
\fBl2arc_headroom_boost\fR (ulong)
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|
.ad
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.RS 12n
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|
Compressed l2arc_headroom multiplier
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|
.sp
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|
Default value: \fB200\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBl2arc_nocompress\fR (int)
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|
.ad
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.RS 12n
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Skip compressing L2ARC buffers
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.sp
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Use \fB1\fR for yes and \fB0\fR for no (default).
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.RE
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.sp
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.ne 2
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.na
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\fBl2arc_noprefetch\fR (int)
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.ad
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.RS 12n
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Skip caching prefetched buffers
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.sp
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Use \fB1\fR for yes (default) and \fB0\fR to disable.
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.RE
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.sp
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.ne 2
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.na
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\fBl2arc_norw\fR (int)
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|
.ad
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.RS 12n
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No reads during writes
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.sp
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Use \fB1\fR for yes and \fB0\fR for no (default).
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.RE
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.sp
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.ne 2
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.na
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\fBl2arc_write_boost\fR (ulong)
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.ad
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.RS 12n
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Extra write bytes during device warmup
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.sp
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|
Default value: \fB8,388,608\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBl2arc_write_max\fR (ulong)
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.ad
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.RS 12n
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Max write bytes per interval
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.sp
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Default value: \fB8,388,608\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBmetaslab_debug\fR (int)
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|
.ad
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.RS 12n
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Keep space maps in core to verify frees
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.sp
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Use \fB1\fR for yes and \fB0\fR for no (default).
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.RE
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.sp
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.ne 2
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.na
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\fBspa_config_path\fR (charp)
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.ad
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.RS 12n
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SPA config file
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|
.sp
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Default value: \fB/etc/zfs/zpool.cache\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBspa_asize_inflation\fR (int)
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.ad
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.RS 12n
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Multiplication factor used to estimate actual disk consumption from the
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size of data being written. The default value is a worst case estimate,
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but lower values may be valid for a given pool depending on its
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configuration. Pool administrators who understand the factors involved
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may wish to specify a more realistic inflation factor, particularly if
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they operate close to quota or capacity limits.
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.sp
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Default value: 24
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.RE
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.sp
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.ne 2
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.na
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\fBzfetch_array_rd_sz\fR (ulong)
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.ad
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.RS 12n
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Number of bytes in a array_read
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.sp
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Default value: \fB1,048,576\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBzfetch_block_cap\fR (uint)
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.ad
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.RS 12n
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Max number of blocks to fetch at a time
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.sp
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Default value: \fB256\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBzfetch_max_streams\fR (uint)
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.ad
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.RS 12n
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Max number of streams per zfetch
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.sp
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Default value: \fB8\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBzfetch_min_sec_reap\fR (uint)
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.ad
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.RS 12n
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Min time before stream reclaim
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.sp
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Default value: \fB2\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBzfs_arc_grow_retry\fR (int)
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.ad
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.RS 12n
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Seconds before growing arc size
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.sp
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Default value: \fB5\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBzfs_arc_max\fR (ulong)
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.ad
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.RS 12n
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Max arc size
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.sp
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Default value: \fB0\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBzfs_arc_memory_throttle_disable\fR (int)
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.ad
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.RS 12n
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Disable memory throttle
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.sp
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Use \fB1\fR for yes (default) and \fB0\fR to disable.
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.RE
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.sp
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.ne 2
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.na
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\fBzfs_arc_meta_limit\fR (ulong)
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.ad
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.RS 12n
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Meta limit for arc size
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.sp
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|
Default value: \fB0\fR.
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.RE
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|
.sp
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.ne 2
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.na
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\fBzfs_arc_meta_prune\fR (int)
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.ad
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.RS 12n
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Bytes of meta data to prune
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.sp
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|
Default value: \fB1,048,576\fR.
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.RE
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|
.sp
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.ne 2
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.na
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\fBzfs_arc_min\fR (ulong)
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.ad
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.RS 12n
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Min arc size
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.sp
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|
Default value: \fB100\fR.
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.RE
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|
.sp
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.ne 2
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.na
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\fBzfs_arc_min_prefetch_lifespan\fR (int)
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.ad
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.RS 12n
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Min life of prefetch block
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.sp
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|
Default value: \fB100\fR.
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.RE
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|
.sp
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.ne 2
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.na
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\fBzfs_arc_p_min_shift\fR (int)
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.ad
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.RS 12n
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arc_c shift to calc min/max arc_p
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|
.sp
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|
Default value: \fB4\fR.
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.RE
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|
.sp
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.ne 2
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.na
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|
\fBzfs_arc_shrink_shift\fR (int)
|
|
.ad
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.RS 12n
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log2(fraction of arc to reclaim)
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|
.sp
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|
Default value: \fB5\fR.
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.RE
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|
.sp
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.ne 2
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.na
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|
\fBzfs_autoimport_disable\fR (int)
|
|
.ad
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.RS 12n
|
|
Disable pool import at module load
|
|
.sp
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|
Use \fB1\fR for yes and \fB0\fR for no (default).
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.RE
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|
|
.sp
|
|
.ne 2
|
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.na
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|
\fBzfs_dbuf_state_index\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Calculate arc header index
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|
.sp
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|
Default value: \fB0\fR.
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.RE
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|
|
|
.sp
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.ne 2
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.na
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|
\fBzfs_deadman_enabled\fR (int)
|
|
.ad
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.RS 12n
|
|
Enable deadman timer
|
|
.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR to disable.
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.RE
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|
.sp
|
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.ne 2
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.na
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|
\fBzfs_deadman_synctime_ms\fR (ulong)
|
|
.ad
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.RS 12n
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|
Expiration time in milliseconds. This value has two meanings. First it is
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|
used to determine when the spa_deadman() logic should fire. By default the
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spa_deadman() will fire if spa_sync() has not completed in 1000 seconds.
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Secondly, the value determines if an I/O is considered "hung". Any I/O that
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has not completed in zfs_deadman_synctime_ms is considered "hung" resulting
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in a zevent being logged.
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.sp
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|
Default value: \fB1,000,000\fR.
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.RE
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|
.sp
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.ne 2
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.na
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\fBzfs_dedup_prefetch\fR (int)
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|
.ad
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.RS 12n
|
|
Enable prefetching dedup-ed blks
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.sp
|
|
Use \fB1\fR for yes (default) and \fB0\fR to disable.
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.RE
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|
.sp
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.ne 2
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.na
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\fBzfs_delay_min_dirty_percent\fR (int)
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.ad
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.RS 12n
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|
Start to delay each transaction once there is this amount of dirty data,
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expressed as a percentage of \fBzfs_dirty_data_max\fR.
|
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This value should be >= zfs_vdev_async_write_active_max_dirty_percent.
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See the section "ZFS TRANSACTION DELAY".
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.sp
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|
Default value: \fB60\fR.
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.RE
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|
|
.sp
|
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.ne 2
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.na
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|
\fBzfs_delay_scale\fR (int)
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.ad
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.RS 12n
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This controls how quickly the transaction delay approaches infinity.
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Larger values cause longer delays for a given amount of dirty data.
|
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.sp
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|
For the smoothest delay, this value should be about 1 billion divided
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by the maximum number of operations per second. This will smoothly
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handle between 10x and 1/10th this number.
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.sp
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See the section "ZFS TRANSACTION DELAY".
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.sp
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Note: \fBzfs_delay_scale\fR * \fBzfs_dirty_data_max\fR must be < 2^64.
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.sp
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Default value: \fB500,000\fR.
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.RE
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.sp
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.ne 2
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.na
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\fBzfs_dirty_data_max\fR (int)
|
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.ad
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.RS 12n
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|
Determines the dirty space limit in bytes. Once this limit is exceeded, new
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writes are halted until space frees up. This parameter takes precedence
|
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over \fBzfs_dirty_data_max_percent\fR.
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See the section "ZFS TRANSACTION DELAY".
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.sp
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Default value: 10 percent of all memory, capped at \fBzfs_dirty_data_max_max\fR.
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.RE
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|
|
.sp
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.ne 2
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.na
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\fBzfs_dirty_data_max_max\fR (int)
|
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.ad
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.RS 12n
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|
Maximum allowable value of \fBzfs_dirty_data_max\fR, expressed in bytes.
|
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This limit is only enforced at module load time, and will be ignored if
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\fBzfs_dirty_data_max\fR is later changed. This parameter takes
|
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precedence over \fBzfs_dirty_data_max_max_percent\fR. See the section
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"ZFS TRANSACTION DELAY".
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.sp
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Default value: 25% of physical RAM.
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.RE
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|
|
.sp
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.ne 2
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.na
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\fBzfs_dirty_data_max_max_percent\fR (int)
|
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.ad
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.RS 12n
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Maximum allowable value of \fBzfs_dirty_data_max\fR, expressed as a
|
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percentage of physical RAM. This limit is only enforced at module load
|
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time, and will be ignored if \fBzfs_dirty_data_max\fR is later changed.
|
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The parameter \fBzfs_dirty_data_max_max\fR takes precedence over this
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one. See the section "ZFS TRANSACTION DELAY".
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.sp
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Default value: 25
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.RE
|
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|
|
.sp
|
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.ne 2
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.na
|
|
\fBzfs_dirty_data_max_percent\fR (int)
|
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.ad
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.RS 12n
|
|
Determines the dirty space limit, expressed as a percentage of all
|
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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".
|
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.sp
|
|
Default value: 10%, subject to \fBzfs_dirty_data_max_max\fR.
|
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.RE
|
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|
|
.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_vdev_async_read_max_active\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Maxium 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
|
|
Maxium 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
|
|
Maxium 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
|
|
Maxium 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
|
|
Maxium 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_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_flags\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Set additional debugging flags
|
|
.sp
|
|
Default value: \fB1\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_free_min_time_ms\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Min millisecs to free 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
|
|
.sp
|
|
Default value: \fB32,768\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_no_scrub_io\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Set for no scrub I/O
|
|
.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 for no scrub prefetching
|
|
.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 flushes
|
|
.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_blks_max\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Max number of blocks to prefetch
|
|
.sp
|
|
Default value: \fB100\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_prefetch_disable\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Disable all ZFS prefetching
|
|
.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
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.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 resilver
|
|
.sp
|
|
Default value: \fB2\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_resilver_min_time_ms\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Min millisecs to resilver per txg
|
|
.sp
|
|
Default value: \fB3,000\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_scan_idle\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Idle window in clock ticks
|
|
.sp
|
|
Default value: \fB50\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_scan_min_time_ms\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Min millisecs to scrub per txg
|
|
.sp
|
|
Default value: \fB1,000\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_scrub_delay\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Number of ticks to delay scrub
|
|
.sp
|
|
Default value: \fB4\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_send_corrupt_data\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Allow to send 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
|
|
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 bps starting in this pass
|
|
.sp
|
|
Default value: \fB2\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_top_maxinflight\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Max I/Os per top-level
|
|
.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
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_txg_timeout\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Max seconds worth of delta per txg
|
|
.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.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_cache_max\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Inflate reads small than max
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_cache_size\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Total size of the per-disk cache
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_mirror_switch_us\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Switch mirrors every N usecs
|
|
.sp
|
|
Default value: \fB10,000\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_read_gap_limit\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Aggregate read I/O over gap
|
|
.sp
|
|
Default value: \fB32,768\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzfs_vdev_scheduler\fR (charp)
|
|
.ad
|
|
.RS 12n
|
|
I/O 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_zevent_cols\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Max event column 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
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzil_replay_disable\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Disable intent logging replay
|
|
.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_bulk_flags\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Additional flags to pass to bulk buffers
|
|
.sp
|
|
Default value: \fB0\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzio_delay_max\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Max zio millisec delay before posting event
|
|
.sp
|
|
Default value: \fB30,000\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzio_injection_enabled\fR (int)
|
|
.ad
|
|
.RS 12n
|
|
Enable fault injection
|
|
.sp
|
|
Use \fB1\fR for yes and \fB0\fR for no (default).
|
|
.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
|
|
\fBzvol_inhibit_dev\fR (uint)
|
|
.ad
|
|
.RS 12n
|
|
Do not create zvol device nodes
|
|
.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 device
|
|
.sp
|
|
Default value: \fB230\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzvol_max_discard_blocks\fR (ulong)
|
|
.ad
|
|
.RS 12n
|
|
Max number of blocks to discard at once
|
|
.sp
|
|
Default value: \fB16,384\fR.
|
|
.RE
|
|
|
|
.sp
|
|
.ne 2
|
|
.na
|
|
\fBzvol_threads\fR (uint)
|
|
.ad
|
|
.RS 12n
|
|
Number of threads for zvol device
|
|
.sp
|
|
Default value: \fB32\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.
|