'\" te
.\" Copyright (c) 2013 by Turbo Fredriksson <turbo@bayour.com>. All rights reserved.
+.\" Copyright (c) 2017 Datto Inc.
.\" The contents of this file are subject to the terms of the Common Development
.\" and Distribution License (the "License"). You may not use this file except
.\" in compliance with the License. You can obtain a copy of the license at
.\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your
.\" own identifying information:
.\" Portions Copyright [yyyy] [name of copyright owner]
-.TH ZFS-MODULE-PARAMETERS 5 "Nov 16, 2013"
+.TH ZFS-MODULE-PARAMETERS 5 "Oct 28, 2017"
.SH NAME
zfs\-module\-parameters \- ZFS module parameters
.SH DESCRIPTION
\fBl2arc_write_boost\fR (ulong)
.ad
.RS 12n
-Cold L2ARC devices will have \fBl2arc_write_nax\fR increased by this amount
+Cold L2ARC devices will have \fBl2arc_write_max\fR increased by this amount
while they remain cold.
.sp
Default value: \fB8,388,608\fR.
.ad
.RS 12n
When using segment-based metaslab selection, continue allocating
-from the active metaslab until \fBlzfs_metaslab_switch_threshold\fR
+from the active metaslab until \fBzfs_metaslab_switch_threshold\fR
worth of buckets have been exhausted.
.sp
Default value: \fB2\fR.
.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
+value acts as a ceiling to the amount of dnode metadata, and defaults to 0 which
indicates that a percent which is based on \fBzfs_arc_dnode_limit_percent\fR of
the ARC meta buffers that may be used for dnodes.
\fBzfs_arc_grow_retry\fR (int)
.ad
.RS 12n
-After a memory pressure event the ARC will wait this many seconds before trying
-to resume growth
+If set to a non zero value, it will replace the arc_grow_retry value with this value.
+The arc_grow_retry value (default 5) is the number of seconds the ARC will wait before
+trying to resume growth after a memory pressure event.
.sp
-Default value: \fB5\fR.
+Default value: \fB0\fR.
.RE
.sp
Default value: \fB0\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_arc_meta_adjust_restarts\fR (ulong)
+.ad
+.RS 12n
+The number of restart passes to make while scanning the ARC attempting
+the free buffers in order to stay below the \fBzfs_arc_meta_limit\fR.
+This value should not need to be tuned but is available to facilitate
+performance analysis.
+.sp
+Default value: \fB4096\fR.
+.RE
+
.sp
.ne 2
.na
.sp
.ne 2
.na
-\fBzfs_arc_meta_adjust_restarts\fR (ulong)
+\fBzfs_arc_meta_strategy\fR (int)
.ad
.RS 12n
-The number of restart passes to make while scanning the ARC attempting
-the free buffers in order to stay below the \fBzfs_arc_meta_limit\fR.
-This value should not need to be tuned but is available to facilitate
-performance analysis.
+Define the strategy for ARC meta data buffer eviction (meta reclaim strategy).
+A value of 0 (META_ONLY) will evict only the ARC meta data buffers.
+A value of 1 (BALANCED) indicates that additional data buffers may be evicted if
+that is required to in order to evict the required number of meta data buffers.
.sp
-Default value: \fB4096\fR.
+Default value: \fB1\fR.
.RE
.sp
\fBzfs_arc_min\fR (ulong)
.ad
.RS 12n
-Min arc size
+Min arc size of ARC in bytes. If set to 0 then arc_c_min will default to
+consuming the larger of 32M or 1/32 of total system memory.
.sp
-Default value: \fB100\fR.
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_arc_min_prefetch_lifespan\fR (int)
+\fBzfs_arc_min_prefetch_ms\fR (int)
.ad
.RS 12n
-Minimum time prefetched blocks are locked in the ARC, specified in jiffies.
-A value of 0 will default to 1 second.
+Minimum time prefetched blocks are locked in the ARC, specified in ms.
+A value of \fB0\fR will default to 1 second.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_min_prescient_prefetch_ms\fR (int)
+.ad
+.RS 12n
+Minimum time "prescient prefetched" blocks are locked in the ARC, specified
+in ms. These blocks are meant to be prefetched fairly aggresively ahead of
+the code that may use them. A value of \fB0\fR will default to 6 seconds.
.sp
Default value: \fB0\fR.
.RE
\fBzfs_arc_p_min_shift\fR (int)
.ad
.RS 12n
-arc_c shift to calc min/max arc_p
+If set to a non zero value, this will update arc_p_min_shift (default 4)
+with the new value.
+arc_p_min_shift is used to shift of arc_c for calculating both min and max
+max arc_p
.sp
-Default value: \fB4\fR.
+Default value: \fB0\fR.
.RE
.sp
\fBzfs_arc_shrink_shift\fR (int)
.ad
.RS 12n
-log2(fraction of arc to reclaim)
+If set to a non zero value, this will update arc_shrink_shift (default 7)
+with the new value.
.sp
-Default value: \fB5\fR.
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_pc_percent\fR (uint)
+.ad
+.RS 12n
+Percent of pagecache to reclaim arc to
+
+This tunable allows ZFS arc to play more nicely with the kernel's LRU
+pagecache. It can guarantee that the arc size won't collapse under scanning
+pressure on the pagecache, yet still allows arc to be reclaimed down to
+zfs_arc_min if necessary. This value is specified as percent of pagecache
+size (as measured by NR_FILE_PAGES) where that percent may exceed 100. This
+only operates during memory pressure/reclaim.
+.sp
+Default value: \fB0\fR (disabled).
.RE
.sp
Use \fB1\fR for yes (default) and \fB0\fR for no.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_commit_timeout_pct\fR (int)
+.ad
+.RS 12n
+This controls the amount of time that a ZIL block (lwb) will remain "open"
+when it isn't "full", and it has a thread waiting for it to be committed to
+stable storage. The timeout is scaled based on a percentage of the last lwb
+latency to avoid significantly impacting the latency of each individual
+transaction record (itx).
+.sp
+Default value: \fB5\fR.
+.RE
+
.sp
.ne 2
.na
Minimum asynchronous write I/Os active to each device.
See the section "ZFS I/O SCHEDULER".
.sp
-Default value: \fB1\fR.
+Lower values are associated with better latency on rotational media but poorer
+resilver performance. The default value of 2 was chosen as a compromise. A
+value of 3 has been shown to improve resilver performance further at a cost of
+further increasing latency.
+.sp
+Default value: \fB2\fR.
.RE
.sp
\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.
+Maximum number of queued allocations per top-level vdev expressed as
+a percentage of \fBzfs_vdev_async_write_max_active\fR which allows the
+system to detect devices that are more capable of handling allocations
+and to allocate more blocks to those devices. It allows for dynamic
+allocation distribution when devices are imbalanced as fuller devices
+will tend to be slower than empty devices.
+
+See also \fBzio_dva_throttle_enabled\fR.
.sp
Default value: \fB1000\fR.
.RE
_
128 ZFS_DEBUG_HISTOGRAM_VERIFY
Enable extra spacemap histogram verifications.
+_
+256 ZFS_DEBUG_METASLAB_VERIFY
+ Verify space accounting on disk matches in-core range_trees.
+_
+512 ZFS_DEBUG_SET_ERROR
+ Enable SET_ERROR and dprintf entries in the debug log.
.TE
.sp
* Requires debug build.
allocations. The default value of 0 disables the feature and causes
all metaslab groups to be eligible for allocations.
-This parameter allows to deal with pools having heavily imbalanced
+This parameter allows one to deal with pools having heavily imbalanced
vdevs such as would be the case when a new vdev has been added.
Setting the threshold to a non-zero percentage will stop allocations
from being made to vdevs that aren't filled to the specified percentage
Default value: \fB0\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_multihost_history\fR (int)
+.ad
+.RS 12n
+Historical statistics for the last N multihost updates will be available in
+\fB/proc/spl/kstat/zfs/<pool>/multihost\fR
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_multihost_interval\fR (ulong)
+.ad
+.RS 12n
+Used to control the frequency of multihost writes which are performed when the
+\fBmultihost\fR pool property is on. This is one factor used to determine
+the length of the activity check during import.
+.sp
+The multihost write period is \fBzfs_multihost_interval / leaf-vdevs\fR milliseconds.
+This means that on average a multihost write will be issued for each leaf vdev every
+\fBzfs_multihost_interval\fR milliseconds. In practice, the observed period can
+vary with the I/O load and this observed value is the delay which is stored in
+the uberblock.
+.sp
+On import the activity check waits a minimum amount of time determined by
+\fBzfs_multihost_interval * zfs_multihost_import_intervals\fR. The activity
+check time may be further extended if the value of mmp delay found in the best
+uberblock indicates actual multihost updates happened at longer intervals than
+\fBzfs_multihost_interval\fR. A minimum value of \fB100ms\fR is enforced.
+.sp
+Default value: \fB1000\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_multihost_import_intervals\fR (uint)
+.ad
+.RS 12n
+Used to control the duration of the activity test on import. Smaller values of
+\fBzfs_multihost_import_intervals\fR will reduce the import time but increase
+the risk of failing to detect an active pool. The total activity check time is
+never allowed to drop below one second. A value of 0 is ignored and treated as
+if it was set to 1
+.sp
+Default value: \fB10\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_multihost_fail_intervals\fR (uint)
+.ad
+.RS 12n
+Controls the behavior of the pool when multihost write failures are detected.
+.sp
+When \fBzfs_multihost_fail_intervals = 0\fR then multihost write failures are ignored.
+The failures will still be reported to the ZED which depending on its
+configuration may take action such as suspending the pool or offlining a device.
+.sp
+When \fBzfs_multihost_fail_intervals > 0\fR then sequential multihost write failures
+will cause the pool to be suspended. This occurs when
+\fBzfs_multihost_fail_intervals * zfs_multihost_interval\fR milliseconds have
+passed since the last successful multihost write. This guarantees the activity test
+will see multihost writes if the pool is imported.
+.sp
+Default value: \fB5\fR.
+.RE
+
.sp
.ne 2
.na
Use \fB1\fR for yes (default) and \fB0\fR to disable.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_dmu_offset_next_sync\fR (int)
+.ad
+.RS 12n
+Enable forcing txg sync to find holes. When enabled forces ZFS to act
+like prior versions when SEEK_HOLE or SEEK_DATA flags are used, which
+when a dnode is dirty causes txg's to be synced so that this data can be
+found.
+.sp
+Use \fB1\fR for yes and \fB0\fR to disable (default).
+.RE
+
.sp
.ne 2
.na
\fBzfs_read_history\fR (int)
.ad
.RS 12n
-Historic statistics for the last N reads will be available in
-\fR/proc/spl/kstat/zfs/POOLNAME/reads\fB
+Historical statistics for the last N reads will be available in
+\fB/proc/spl/kstat/zfs/<pool>/reads\fR
.sp
Default value: \fB0\fR (no data is kept).
.RE
.sp
.ne 2
.na
-\fBzfs_resilver_delay\fR (int)
+\fBzfs_resilver_min_time_ms\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.
+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: \fB2\fR.
+Default value: \fB3,000\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_resilver_min_time_ms\fR (int)
+\fBzfs_scrub_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.
+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: \fB3,000\fR.
+Default value: \fB1,000\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_scan_idle\fR (int)
+\fBzfs_scan_checkpoint_intval\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.
+To preserve progress across reboots the sequential scan algorithm periodically
+needs to stop metadata scanning and issue all the verifications I/Os to disk.
+The frequency of this flushing is determined by the
+\fBfBzfs_scan_checkpoint_intval\fR tunable.
.sp
-Default value: \fB50\fR.
+Default value: \fB7200\fR seconds (every 2 hours).
.RE
.sp
.ne 2
.na
-\fBzfs_scan_min_time_ms\fR (int)
+\fBzfs_scan_fill_weight\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.
+This tunable affects how scrub and resilver I/O segments are ordered. A higher
+number indicates that we care more about how filled in a segment is, while a
+lower number indicates we care more about the size of the extent without
+considering the gaps within a segment. This value is only tunable upon module
+insertion. Changing the value afterwards will have no affect on scrub or
+resilver performance.
.sp
-Default value: \fB1,000\fR.
+Default value: \fB3\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_issue_strategy\fR (int)
+.ad
+.RS 12n
+Determines the order that data will be verified while scrubbing or resilvering.
+If set to \fB1\fR, data will be verified as sequentially as possible, given the
+amount of memory reserved for scrubbing (see \fBzfs_scan_mem_lim_fact\fR). This
+may improve scrub performance if the pool's data is very fragmented. If set to
+\fB2\fR, the largest mostly-contiguous chunk of found data will be verified
+first. By deferring scrubbing of small segments, we may later find adjacent data
+to coalesce and increase the segment size. If set to \fB0\fR, zfs will use
+strategy \fB1\fR during normal verification and strategy \fB2\fR while taking a
+checkpoint.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_legacy\fR (int)
+.ad
+.RS 12n
+A value of 0 indicates that scrubs and resilvers will gather metadata in
+memory before issuing sequential I/O. A value of 1 indicates that the legacy
+algorithm will be used where I/O is initiated as soon as it is discovered.
+Changing this value to 0 will not affect scrubs or resilvers that are already
+in progress.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_max_ext_gap\fR (int)
+.ad
+.RS 12n
+Indicates the largest gap in bytes between scrub / resilver I/Os that will still
+be considered sequential for sorting purposes. Changing this value will not
+affect scrubs or resilvers that are already in progress.
+.sp
+Default value: \fB2097152 (2 MB)\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_scrub_delay\fR (int)
+\fBzfs_scan_mem_lim_fact\fR (int)
.ad
.RS 12n
-Number of ticks to delay prior to issuing a scrub I/O operation when
-a non-scrub or non-resilver I/O operation has occurred within the past
-\fBzfs_scan_idle\fR ticks.
+Maximum fraction of RAM used for I/O sorting by sequential scan algorithm.
+This tunable determines the hard limit for I/O sorting memory usage.
+When the hard limit is reached we stop scanning metadata and start issuing
+data verification I/O. This is done until we get below the soft limit.
.sp
-Default value: \fB4\fR.
+Default value: \fB20\fR which is 5% of RAM (1/20).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_mem_lim_soft_fact\fR (int)
+.ad
+.RS 12n
+The fraction of the hard limit used to determined the soft limit for I/O sorting
+by the sequential scan algorithm. When we cross this limit from bellow no action
+is taken. When we cross this limit from above it is because we are issuing
+verification I/O. In this case (unless the metadata scan is done) we stop
+issuing verification I/O and start scanning metadata again until we get to the
+hard limit.
+.sp
+Default value: \fB20\fR which is 5% of the hard limit (1/20).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_scan_vdev_limit\fR (int)
+.ad
+.RS 12n
+Maximum amount of data that can be concurrently issued at once for scrubs and
+resilvers per leaf device, given in bytes.
+.sp
+Default value: \fB41943040\fR.
.RE
.sp
.sp
.ne 2
.na
-\fBzfs_top_maxinflight\fR (int)
+\fBzfs_sync_taskq_batch_pct\fR (int)
.ad
.RS 12n
-Max concurrent I/Os per top-level vdev (mirrors or raidz arrays) allowed during
-scrub or resilver operations.
+This controls the number of threads used by the dp_sync_taskq. The default
+value of 75% will create a maximum of one thread per cpu.
.sp
-Default value: \fB32\fR.
+Default value: \fB75\fR.
.RE
.sp
\fBzfs_txg_history\fR (int)
.ad
.RS 12n
-Historic statistics for the last N txgs will be available in
-\fR/proc/spl/kstat/zfs/POOLNAME/txgs\fB
+Historical statistics for the last N txgs will be available in
+\fB/proc/spl/kstat/zfs/<pool>/txgs\fR
.sp
Default value: \fB0\fR.
.RE
\fBzfs_vdev_cache_max\fR (int)
.ad
.RS 12n
-Inflate reads small than this value to meet the \fBzfs_vdev_cache_bshift\fR
-size.
+Inflate reads smaller than this value to meet the \fBzfs_vdev_cache_bshift\fR
+size (default 64k).
.sp
Default value: \fB16384\fR.
.RE
\fBzfs_vdev_scheduler\fR (charp)
.ad
.RS 12n
-Set the Linux I/O scheduler on whole disk vdevs to this scheduler
+Set the Linux I/O scheduler on whole disk vdevs to this scheduler. Valid options
+are noop, cfq, bfq & deadline
.sp
Default value: \fBnoop\fR.
.RE
Default value: \fB0\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_zil_clean_taskq_maxalloc\fR (int)
+.ad
+.RS 12n
+The maximum number of taskq entries that are allowed to be cached. When this
+limit is exceeded transaction records (itxs) will be cleaned synchronously.
+.sp
+Default value: \fB1048576\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_zil_clean_taskq_minalloc\fR (int)
+.ad
+.RS 12n
+The number of taskq entries that are pre-populated when the taskq is first
+created and are immediately available for use.
+.sp
+Default value: \fB1024\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_zil_clean_taskq_nthr_pct\fR (int)
+.ad
+.RS 12n
+This controls the number of threads used by the dp_zil_clean_taskq. The default
+value of 100% will create a maximum of one thread per cpu.
+.sp
+Default value: \fB100\fR.
+.RE
+
.sp
.ne 2
.na
.sp
.ne 2
.na
-\fBzil_slog_limit\fR (ulong)
+\fBzil_slog_bulk\fR (ulong)
.ad
.RS 12n
-Max commit bytes to separate log device
+Limit SLOG write size per commit executed with synchronous priority.
+Any writes above that will be executed with lower (asynchronous) priority
+to limit potential SLOG device abuse by single active ZIL writer.
.sp
-Default value: \fB1,048,576\fR.
+Default value: \fB786,432\fR.
.RE
.sp
.RS 12n
Throttle block allocations in the ZIO pipeline. This allows for
dynamic allocation distribution when devices are imbalanced.
+When enabled, the maximum number of pending allocations per top-level vdev
+is limited by \fBzfs_vdev_queue_depth_pct\fR.
.sp
Default value: \fB1\fR.
.RE
Default value: \fB131,072\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzvol_request_sync\fR (uint)
+.ad
+.RS 12n
+When processing I/O requests for a zvol submit them synchronously. This
+effectively limits the queue depth to 1 for each I/O submitter. When set
+to 0 requests are handled asynchronously by a thread pool. The number of
+requests which can be handled concurrently is controller by \fBzvol_threads\fR.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzvol_threads\fR (uint)
+.ad
+.RS 12n
+Max number of threads which can handle zvol I/O requests concurrently.
+.sp
+Default value: \fB32\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzvol_volmode\fR (uint)
+.ad
+.RS 12n
+Defines zvol block devices behaviour when \fBvolmode\fR is set to \fBdefault\fR.
+Valid values are \fB1\fR (full), \fB2\fR (dev) and \fB3\fR (none).
+.sp
+Default value: \fB1\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_qat_disable\fR (int)
+.ad
+.RS 12n
+This tunable disables qat hardware acceleration for gzip compression.
+It is available only if qat acceleration is compiled in and qat driver
+is present.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
.SH ZFS I/O SCHEDULER
ZFS issues I/O operations to leaf vdevs to satisfy and complete I/Os.
The I/O scheduler determines when and in what order those operations are
projects / mirror_zfs.git / blobdiff