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Move properties, parameters, events, and concepts around manual sections

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The pages moved as follows:
  zpool-features.{5 => 7}
  spl{-module-parameters.5 => .4}
  zfs{-module-parameters.5 => .4}
  zfs-events.5 => into zpool-events.8
  zfsconcepts.{8 => 7}
  zfsprops.{8 => 7}
  zpoolconcepts.{8 => 7}
  zpoolprops.{8 => 7}

Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Co-authored-by: Daniel Ebdrup Jensen <debdrup@FreeBSD.org>
Closes #12149
Closes #12212
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2021-06-04 22:29:26 +02:00
committed by Brian Behlendorf
parent b0f3e8a6eb
commit 2badb3457a
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man/man5/spl-module-parameters.5
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.\"
.\" 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
.\" usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.
.\"
.\" See the License for the specific language governing permissions and
.\" limitations under the License. When distributing Covered Code, include this
.\" CDDL HEADER in each file and include the License file at
.\" usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this
.\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your
.\" own identifying information:
.\" Portions Copyright [yyyy] [name of copyright owner]
.\"
.\" Copyright 2013 Turbo Fredriksson <turbo@bayour.com>. All rights reserved.
.\"
.Dd August 24, 2020
.Dt SPL-MODULE-PARAMETERS 5
.Os
.
.Sh NAME
.Nm spl-module-parameters
.Nd parameters of the SPL kernel module
.
.Sh DESCRIPTION
.Bl -tag -width Ds
.It Sy spl_kmem_cache_kmem_threads Ns = Ns Sy 4 Pq uint
The number of threads created for the spl_kmem_cache task queue.
This task queue is responsible for allocating new slabs
for use by the kmem caches.
For the majority of systems and workloads only a small number of threads are
required.
.
.It Sy spl_kmem_cache_reclaim Ns = Ns Sy 0 Pq uint
When this is set it prevents Linux from being able to rapidly reclaim all the
memory held by the kmem caches.
This may be useful in circumstances where it's preferable that Linux
reclaim memory from some other subsystem first.
Setting this will increase the likelihood out of memory events on a memory
constrained system.
.
.It Sy spl_kmem_cache_obj_per_slab Ns = Ns Sy 8 Pq uint
The preferred number of objects per slab in the cache.
In general, a larger value will increase the caches memory footprint
while decreasing the time required to perform an allocation.
Conversely, a smaller value will minimize the footprint
and improve cache reclaim time but individual allocations may take longer.
.
.It Sy spl_kmem_cache_max_size Ns = Ns Sy 32 Po 64-bit Pc or Sy 4 Po 32-bit Pc Pq uint
The maximum size of a kmem cache slab in MiB.
This effectively limits the maximum cache object size to
.Sy spl_kmem_cache_max_size Ns / Ns Sy spl_kmem_cache_obj_per_slab .
.Pp
Caches may not be created with
object sized larger than this limit.
.
.It Sy spl_kmem_cache_slab_limit Ns = Ns Sy 16384 Pq uint
For small objects the Linux slab allocator should be used to make the most
efficient use of the memory.
However, large objects are not supported by
the Linux slab and therefore the SPL implementation is preferred.
This value is used to determine the cutoff between a small and large object.
.Pp
Objects of size
.Sy spl_kmem_cache_slab_limit
or smaller will be allocated using the Linux slab allocator,
large objects use the SPL allocator.
A cutoff of 16K was determined to be optimal for architectures using 4K pages.
.
.It Sy spl_kmem_alloc_warn Ns = Ns Sy 32768 Pq uint
As a general rule
.Fn kmem_alloc
allocations should be small,
preferably just a few pages, since they must by physically contiguous.
Therefore, a rate limited warning will be printed to the console for any
.Fn kmem_alloc
which exceeds a reasonable threshold.
.Pp
The default warning threshold is set to eight pages but capped at 32K to
accommodate systems using large pages.
This value was selected to be small enough to ensure
the largest allocations are quickly noticed and fixed.
But large enough to avoid logging any warnings when a allocation size is
larger than optimal but not a serious concern.
Since this value is tunable, developers are encouraged to set it lower
when testing so any new largish allocations are quickly caught.
These warnings may be disabled by setting the threshold to zero.
.
.It Sy spl_kmem_alloc_max Ns = Ns Sy KMALLOC_MAX_SIZE Ns / Ns Sy 4 Pq uint
Large
.Fn kmem_alloc
allocations will fail if they exceed
.Sy KMALLOC_MAX_SIZE .
Allocations which are marginally smaller than this limit may succeed but
should still be avoided due to the expense of locating a contiguous range
of free pages.
Therefore, a maximum kmem size with reasonable safely margin of 4x is set.
.Fn kmem_alloc
allocations larger than this maximum will quickly fail.
.Fn vmem_alloc
allocations less than or equal to this value will use
.Fn kmalloc ,
but shift to
.Fn vmalloc
when exceeding this value.
.
.It Sy spl_kmem_cache_magazine_size Ns = Ns Sy 0 Pq uint
Cache magazines are an optimization designed to minimize the cost of
allocating memory.
They do this by keeping a per-cpu cache of recently
freed objects, which can then be reallocated without taking a lock.
This can improve performance on highly contended caches.
However, because objects in magazines will prevent otherwise empty slabs
from being immediately released this may not be ideal for low memory machines.
.Pp
For this reason,
.Sy spl_kmem_cache_magazine_size
can be used to set a maximum magazine size.
When this value is set to 0 the magazine size will
be automatically determined based on the object size.
Otherwise magazines will be limited to 2-256 objects per magazine (i.e per cpu).
Magazines may never be entirely disabled in this implementation.
.
.It Sy spl_hostid Ns = Ns Sy 0 Pq ulong
The system hostid, when set this can be used to uniquely identify a system.
By default this value is set to zero which indicates the hostid is disabled.
It can be explicitly enabled by placing a unique non-zero value in
.Pa /etc/hostid .
.
.It Sy spl_hostid_path Ns = Ns Pa /etc/hostid Pq charp
The expected path to locate the system hostid when specified.
This value may be overridden for non-standard configurations.
.
.It Sy spl_panic_halt Ns = Ns Sy 0 Pq uint
Cause a kernel panic on assertion failures.
When not enabled, the thread is halted to facilitate further debugging.
.Pp
Set to a non-zero value to enable.
.
.It Sy spl_taskq_kick Ns = Ns Sy 0 Pq uint
Kick stuck taskq to spawn threads.
When writing a non-zero value to it, it will scan all the taskqs.
If any of them have a pending task more than 5 seconds old,
it will kick it to spawn more threads.
This can be used if you find a rare
deadlock occurs because one or more taskqs didn't spawn a thread when it should.
.
.It Sy spl_taskq_thread_bind Ns = Ns Sy 0 Pq int
Bind taskq threads to specific CPUs.
When enabled all taskq threads will be distributed evenly
across the available CPUs.
By default, this behavior is disabled to allow the Linux scheduler
the maximum flexibility to determine where a thread should run.
.
.It Sy spl_taskq_thread_dynamic Ns = Ns Sy 1 Pq int
Allow dynamic taskqs.
When enabled taskqs which set the
.Sy TASKQ_DYNAMIC
flag will by default create only a single thread.
New threads will be created on demand up to a maximum allowed number
to facilitate the completion of outstanding tasks.
Threads which are no longer needed will be promptly destroyed.
By default this behavior is enabled but it can be disabled to
aid performance analysis or troubleshooting.
.
.It Sy spl_taskq_thread_priority Ns = Ns Sy 1 Pq int
Allow newly created taskq threads to set a non-default scheduler priority.
When enabled, the priority specified when a taskq is created will be applied
to all threads created by that taskq.
When disabled all threads will use the default Linux kernel thread priority.
By default, this behavior is enabled.
.
.It Sy spl_taskq_thread_sequential Ns = Ns Sy 4 Pq int
The number of items a taskq worker thread must handle without interruption
before requesting a new worker thread be spawned.
This is used to control
how quickly taskqs ramp up the number of threads processing the queue.
Because Linux thread creation and destruction are relatively inexpensive a
small default value has been selected.
This means that normally threads will be created aggressively which is desirable.
Increasing this value will
result in a slower thread creation rate which may be preferable for some
configurations.
.
.It Sy spl_max_show_tasks Ns = Ns Sy 512 Pq uint
The maximum number of tasks per pending list in each taskq shown in
.Pa /proc/spl/taskq{,-all} .
Write
.Sy 0
to turn off the limit.
The proc file will walk the lists with lock held,
reading it could cause a lock-up if the list grow too large
without limiting the output.
"(truncated)" will be shown if the list is larger than the limit.
.
.El
man/man5/zfs-events.5
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.\"
.\" Copyright (c) 2013 by Turbo Fredriksson <turbo@bayour.com>. All rights reserved.
.\" Portions Copyright 2018 by Richard Elling
.\" 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
.\" usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.
.\"
.\" See the License for the specific language governing permissions and
.\" limitations under the License. When distributing Covered Code, include this
.\" CDDL HEADER in each file and include the License file at
.\" usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this
.\" CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your
.\" own identifying information:
.\" Portions Copyright [yyyy] [name of copyright owner]
.\"
.Dd May 26, 2021
.Dt ZFS-EVENTS 5
.Os
.
.Sh NAME
.Nm zfs-events
.Nd Events created by the ZFS filesystem
.Sh DESCRIPTION
Description of the different events generated by the ZFS stack.
.Pp
Most of these don't have any description.
The events generated by ZFS have never been publicly documented.
What is here is intended as a starting point to provide documentation
for all possible events.
.Pp
To view all events created since the loading of the ZFS infrastructure
(i.e, "the module"), run
.Dl Nm zpool Cm events
to get a short list, and
.Dl Nm zpool Cm events Fl v
to get a full detail of the events and what information
is available about it.
.Pp
This manual page lists the different subclasses that are issued
in the case of an event.
The full event name would be
.Sy ereport.fs.zfs.\& Ns Em SUBCLASS ,
but we only list the last part here.
.
.Sh EVENTS (SUBCLASS)
.Bl -tag -compact -width "vdev.bad_guid_sum"
.It Sy checksum
Issued when a checksum error has been detected.
.It Sy io
Issued when there is an I/O error in a vdev in the pool.
.It Sy data
Issued when there have been data errors in the pool.
.It Sy deadman
Issued when an I/O request is determined to be "hung", this can be caused
by lost completion events due to flaky hardware or drivers.
See
.Sy zfs_deadman_failmode
in
.Xr zfs-module-parameters 5
for additional information regarding "hung" I/O detection and configuration.
.It Sy delay
Issued when a completed I/O request exceeds the maximum allowed time
specified by the
.Sy zio_slow_io_ms
module parameter.
This can be an indicator of problems with the underlying storage device.
The number of delay events is ratelimited by the
.Sy zfs_slow_io_events_per_second
module parameter.
.It Sy config
Issued every time a vdev change have been done to the pool.
.It Sy zpool
Issued when a pool cannot be imported.
.It Sy zpool.destroy
Issued when a pool is destroyed.
.It Sy zpool.export
Issued when a pool is exported.
.It Sy zpool.import
Issued when a pool is imported.
.It Sy zpool.reguid
Issued when a REGUID (new unique identifier for the pool have been regenerated) have been detected.
.It Sy vdev.unknown
Issued when the vdev is unknown.
Such as trying to clear device errors on a vdev that have failed/been kicked
from the system/pool and is no longer available.
.It Sy vdev.open_failed
Issued when a vdev could not be opened (because it didn't exist for example).
.It Sy vdev.corrupt_data
Issued when corrupt data have been detected on a vdev.
.It Sy vdev.no_replicas
Issued when there are no more replicas to sustain the pool.
This would lead to the pool being
.Em DEGRADED .
.It Sy vdev.bad_guid_sum
Issued when a missing device in the pool have been detected.
.It Sy vdev.too_small
Issued when the system (kernel) have removed a device, and ZFS
notices that the device isn't there any more.
This is usually followed by a
.Sy probe_failure
event.
.It Sy vdev.bad_label
Issued when the label is OK but invalid.
.It Sy vdev.bad_ashift
Issued when the ashift alignment requirement has increased.
.It Sy vdev.remove
Issued when a vdev is detached from a mirror (or a spare detached from a
vdev where it have been used to replace a failed drive - only works if
the original drive have been readded).
.It Sy vdev.clear
Issued when clearing device errors in a pool.
Such as running
.Nm zpool Cm clear
on a device in the pool.
.It Sy vdev.check
Issued when a check to see if a given vdev could be opened is started.
.It Sy vdev.spare
Issued when a spare have kicked in to replace a failed device.
.It Sy vdev.autoexpand
Issued when a vdev can be automatically expanded.
.It Sy io_failure
Issued when there is an I/O failure in a vdev in the pool.
.It Sy probe_failure
Issued when a probe fails on a vdev.
This would occur if a vdev
have been kicked from the system outside of ZFS (such as the kernel
have removed the device).
.It Sy log_replay
Issued when the intent log cannot be replayed.
The can occur in the case of a missing or damaged log device.
.It Sy resilver.start
Issued when a resilver is started.
.It Sy resilver.finish
Issued when the running resilver have finished.
.It Sy scrub.start
Issued when a scrub is started on a pool.
.It Sy scrub.finish
Issued when a pool has finished scrubbing.
.It Sy scrub.abort
Issued when a scrub is aborted on a pool.
.It Sy scrub.resume
Issued when a scrub is resumed on a pool.
.It Sy scrub.paused
Issued when a scrub is paused on a pool.
.It Sy bootfs.vdev.attach
.El
.
.Sh PAYLOADS
This is the payload (data, information) that accompanies an
event.
.Pp
For
.Xr zed 8 ,
these are set to uppercase and prefixed with
.Sy ZEVENT_ .
.Bl -tag -compact -width "vdev_cksum_errors"
.It Sy pool
Pool name.
.It Sy pool_failmode
Failmode -
.Sy wait ,
.Sy continue ,
or
.Sy panic .
See the
.Sy failmode
property in
.Xr zpoolprops 8
for more information.
.It Sy pool_guid
The GUID of the pool.
.It Sy pool_context
The load state for the pool (0=none, 1=open, 2=import, 3=tryimport, 4=recover
5=error).
.It Sy vdev_guid
The GUID of the vdev in question (the vdev failing or operated upon with
.Nm zpool Cm clear ,
etc.).
.It Sy vdev_type
Type of vdev -
.Sy disk ,
.Sy file ,
.Sy mirror ,
etc.
See the
.Sy Virtual Devices
section of
.Xr zpoolconcepts 8
for more information on possible values.
.It Sy vdev_path
Full path of the vdev, including any
.Em -partX .
.It Sy vdev_devid
ID of vdev (if any).
.It Sy vdev_fru
Physical FRU location.
.It Sy vdev_state
State of vdev (0=uninitialized, 1=closed, 2=offline, 3=removed, 4=failed to open, 5=faulted, 6=degraded, 7=healthy).
.It Sy vdev_ashift
The ashift value of the vdev.
.It Sy vdev_complete_ts
The time the last I/O request completed for the specified vdev.
.It Sy vdev_delta_ts
The time since the last I/O request completed for the specified vdev.
.It Sy vdev_spare_paths
List of spares, including full path and any
.Em -partX .
.It Sy vdev_spare_guids
GUID(s) of spares.
.It Sy vdev_read_errors
How many read errors that have been detected on the vdev.
.It Sy vdev_write_errors
How many write errors that have been detected on the vdev.
.It Sy vdev_cksum_errors
How many checksum errors that have been detected on the vdev.
.It Sy parent_guid
GUID of the vdev parent.
.It Sy parent_type
Type of parent.
See
.Sy vdev_type .
.It Sy parent_path
Path of the vdev parent (if any).
.It Sy parent_devid
ID of the vdev parent (if any).
.It Sy zio_objset
The object set number for a given I/O request.
.It Sy zio_object
The object number for a given I/O request.
.It Sy zio_level
The indirect level for the block.
Level 0 is the lowest level and includes data blocks.
Values > 0 indicate metadata blocks at the appropriate level.
.It Sy zio_blkid
The block ID for a given I/O request.
.It Sy zio_err
The error number for a failure when handling a given I/O request,
compatible with
.Xr errno 3
with the value of
.Sy EBADE
used to indicate a ZFS checksum error.
.It Sy zio_offset
The offset in bytes of where to write the I/O request for the specified vdev.
.It Sy zio_size
The size in bytes of the I/O request.
.It Sy zio_flags
The current flags describing how the I/O request should be handled.
See the
.Sy I/O FLAGS
section for the full list of I/O flags.
.It Sy zio_stage
The current stage of the I/O in the pipeline.
See the
.Sy I/O STAGES
section for a full list of all the I/O stages.
.It Sy zio_pipeline
The valid pipeline stages for the I/O.
See the
.Sy I/O STAGES
section for a full list of all the I/O stages.
.It Sy zio_delay
The time elapsed (in nanoseconds) waiting for the block layer to complete the
I/O request.
Unlike
.Sy zio_delta ,
this does not include any vdev queuing time and is
therefore solely a measure of the block layer performance.
.It Sy zio_timestamp
The time when a given I/O request was submitted.
.It Sy zio_delta
The time required to service a given I/O request.
.It Sy prev_state
The previous state of the vdev.
.It Sy cksum_expected
The expected checksum value for the block.
.It Sy cksum_actual
The actual checksum value for an errant block.
.It Sy cksum_algorithm
Checksum algorithm used.
See
.Xr zfsprops 8
for more information on the available checksum algorithms.
.It Sy cksum_byteswap
Whether or not the data is byteswapped.
.It Sy bad_ranges
.No [\& Ns Ar start , end )
pairs of corruption offsets.
Offsets are always aligned on a 64-bit boundary,
and can include some gaps of non-corruption.
(See
.Sy bad_ranges_min_gap )
.It Sy bad_ranges_min_gap
In order to bound the size of the
.Sy bad_ranges
array, gaps of non-corruption
less than or equal to
.Sy bad_ranges_min_gap
bytes have been merged with
adjacent corruption.
Always at least 8 bytes, since corruption is detected on a 64-bit word basis.
.It Sy bad_range_sets
This array has one element per range in
.Sy bad_ranges .
Each element contains
the count of bits in that range which were clear in the good data and set
in the bad data.
.It Sy bad_range_clears
This array has one element per range in
.Sy bad_ranges .
Each element contains
the count of bits for that range which were set in the good data and clear in
the bad data.
.It Sy bad_set_bits
If this field exists, it is an array of
.Pq Ar bad data No & ~( Ns Ar good data ) ;
that is, the bits set in the bad data which are cleared in the good data.
Each element corresponds a byte whose offset is in a range in
.Sy bad_ranges ,
and the array is ordered by offset.
Thus, the first element is the first byte in the first
.Sy bad_ranges
range, and the last element is the last byte in the last
.Sy bad_ranges
range.
.It Sy bad_cleared_bits
Like
.Sy bad_set_bits ,
but contains
.Pq Ar good data No & ~( Ns Ar bad data ) ;
that is, the bits set in the good data which are cleared in the bad data.
.It Sy bad_set_histogram
If this field exists, it is an array of counters.
Each entry counts bits set in a particular bit of a big-endian uint64 type.
The first entry counts bits
set in the high-order bit of the first byte, the 9th byte, etc, and the last
entry counts bits set of the low-order bit of the 8th byte, the 16th byte, etc.
This information is useful for observing a stuck bit in a parallel data path,
such as IDE or parallel SCSI.
.It Sy bad_cleared_histogram
If this field exists, it is an array of counters.
Each entry counts bit clears in a particular bit of a big-endian uint64 type.
The first entry counts bits
clears of the high-order bit of the first byte, the 9th byte, etc, and the
last entry counts clears of the low-order bit of the 8th byte, the 16th byte, etc.
This information is useful for observing a stuck bit in a parallel data
path, such as IDE or parallel SCSI.
.El
.
.Sh I/O STAGES
The ZFS I/O pipeline is comprised of various stages which are defined below.
The individual stages are used to construct these basic I/O
operations: Read, Write, Free, Claim, and Ioctl.
These stages may be
set on an event to describe the life cycle of a given I/O request.
.Pp
.TS
tab(:);
l l l .
Stage:Bit Mask:Operations
_:_:_
ZIO_STAGE_OPEN:0x00000001:RWFCI
ZIO_STAGE_READ_BP_INIT:0x00000002:R----
ZIO_STAGE_WRITE_BP_INIT:0x00000004:-W---
ZIO_STAGE_FREE_BP_INIT:0x00000008:--F--
ZIO_STAGE_ISSUE_ASYNC:0x00000010:RWF--
ZIO_STAGE_WRITE_COMPRESS:0x00000020:-W---
ZIO_STAGE_ENCRYPT:0x00000040:-W---
ZIO_STAGE_CHECKSUM_GENERATE:0x00000080:-W---
ZIO_STAGE_NOP_WRITE:0x00000100:-W---
ZIO_STAGE_DDT_READ_START:0x00000200:R----
ZIO_STAGE_DDT_READ_DONE:0x00000400:R----
ZIO_STAGE_DDT_WRITE:0x00000800:-W---
ZIO_STAGE_DDT_FREE:0x00001000:--F--
ZIO_STAGE_GANG_ASSEMBLE:0x00002000:RWFC-
ZIO_STAGE_GANG_ISSUE:0x00004000:RWFC-
ZIO_STAGE_DVA_THROTTLE:0x00008000:-W---
ZIO_STAGE_DVA_ALLOCATE:0x00010000:-W---
ZIO_STAGE_DVA_FREE:0x00020000:--F--
ZIO_STAGE_DVA_CLAIM:0x00040000:---C-
ZIO_STAGE_READY:0x00080000:RWFCI
ZIO_STAGE_VDEV_IO_START:0x00100000:RW--I
ZIO_STAGE_VDEV_IO_DONE:0x00200000:RW--I
ZIO_STAGE_VDEV_IO_ASSESS:0x00400000:RW--I
ZIO_STAGE_CHECKSUM_VERIFY:0x00800000:R----
ZIO_STAGE_DONE:0x01000000:RWFCI
.TE
.
.Sh I/O FLAGS
Every I/O request in the pipeline contains a set of flags which describe its
function and are used to govern its behavior.
These flags will be set in an event as a
.Sy zio_flags
payload entry.
.Pp
.TS
tab(:);
l l .
Flag:Bit Mask
_:_
ZIO_FLAG_DONT_AGGREGATE:0x00000001
ZIO_FLAG_IO_REPAIR:0x00000002
ZIO_FLAG_SELF_HEAL:0x00000004
ZIO_FLAG_RESILVER:0x00000008
ZIO_FLAG_SCRUB:0x00000010
ZIO_FLAG_SCAN_THREAD:0x00000020
ZIO_FLAG_PHYSICAL:0x00000040
ZIO_FLAG_CANFAIL:0x00000080
ZIO_FLAG_SPECULATIVE:0x00000100
ZIO_FLAG_CONFIG_WRITER:0x00000200
ZIO_FLAG_DONT_RETRY:0x00000400
ZIO_FLAG_DONT_CACHE:0x00000800
ZIO_FLAG_NODATA:0x00001000
ZIO_FLAG_INDUCE_DAMAGE:0x00002000
ZIO_FLAG_IO_ALLOCATING:0x00004000
ZIO_FLAG_IO_RETRY:0x00008000
ZIO_FLAG_PROBE:0x00010000
ZIO_FLAG_TRYHARD:0x00020000
ZIO_FLAG_OPTIONAL:0x00040000
ZIO_FLAG_DONT_QUEUE:0x00080000
ZIO_FLAG_DONT_PROPAGATE:0x00100000
ZIO_FLAG_IO_BYPASS:0x00200000
ZIO_FLAG_IO_REWRITE:0x00400000
ZIO_FLAG_RAW_COMPRESS:0x00800000
ZIO_FLAG_RAW_ENCRYPT:0x01000000
ZIO_FLAG_GANG_CHILD:0x02000000
ZIO_FLAG_DDT_CHILD:0x04000000
ZIO_FLAG_GODFATHER:0x08000000
ZIO_FLAG_NOPWRITE:0x10000000
ZIO_FLAG_REEXECUTED:0x20000000
ZIO_FLAG_DELEGATED:0x40000000
ZIO_FLAG_FASTWRITE:0x80000000
.TE
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.\"
.\" Copyright (c) 2012, 2018 by Delphix. All rights reserved.
.\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
.\" Copyright (c) 2014, Joyent, Inc. All rights reserved.
.\" The contents of this file are subject to the terms of the Common Development
.\" and Distribution License (the "License"). You may not use this file except
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.\" Copyright (c) 2019, Allan Jude
.\" Copyright (c) 2021, Colm Buckley <colm@tuatha.org>
.\"
.Dd May 31, 2021
.Dt ZPOOL-FEATURES 5
.Os
.
.Sh NAME
.Nm zpool-features
.Nd description of ZFS pool features
.
.Sh DESCRIPTION
ZFS pool on-disk format versions are specified via "features" which replace
the old on-disk format numbers (the last supported on-disk format number is 28).
To enable a feature on a pool use the
.Nm zpool Cm upgrade ,
or set the
.Sy feature Ns @ Ns Ar feature-name
property to
.Sy enabled .
Please also see the
.Sx Compatibility feature sets
section for information on how sets of features may be enabled together.
.Pp
The pool format does not affect file system version compatibility or the ability
to send file systems between pools.
.Pp
Since most features can be enabled independently of each other, the on-disk
format of the pool is specified by the set of all features marked as
.Sy active
on the pool.
If the pool was created by another software version
this set may include unsupported features.
.
.Ss Identifying features
Every feature has a GUID of the form
.Ar com.example : Ns Ar feature-name .
The reversed DNS name ensures that the feature's GUID is unique across all ZFS
implementations.
When unsupported features are encountered on a pool they will
be identified by their GUIDs.
Refer to the documentation for the ZFS
implementation that created the pool for information about those features.
.Pp
Each supported feature also has a short name.
By convention a feature's short name is the portion of its GUID which follows the
.Sq \&:
(i.e.
.Ar com.example : Ns Ar feature-name
would have the short name
.Ar feature-name ) ,
however a feature's short name may differ across ZFS implementations if
following the convention would result in name conflicts.
.
.Ss Feature states
Features can be in one of three states:
.Bl -tag -width "disabled"
.It Sy active
This feature's on-disk format changes are in effect on the pool.
Support for this feature is required to import the pool in read-write mode.
If this feature is not read-only compatible,
support is also required to import the pool in read-only mode
.Pq see Sx Read-only compatibility .
.It Sy enabled
An administrator has marked this feature as enabled on the pool, but the
feature's on-disk format changes have not been made yet.
The pool can still be imported by software that does not support this feature,
but changes may be made to the on-disk format at any time
which will move the feature to the
.Sy active
state.
Some features may support returning to the
.Sy enabled
state after becoming
.Sy active .
See feature-specific documentation for details.
.It Sy disabled
This feature's on-disk format changes have not been made and will not be made
unless an administrator moves the feature to the
.Sy enabled
state.
Features cannot be disabled once they have been enabled.
.El
.Pp
The state of supported features is exposed through pool properties of the form
.Sy feature Ns @ Ns Ar short-name .
.
.Ss Read-only compatibility
Some features may make on-disk format changes that do not interfere with other
software's ability to read from the pool.
These features are referred to as
.Dq read-only compatible .
If all unsupported features on a pool are read-only compatible,
the pool can be imported in read-only mode by setting the
.Sy readonly
property during import (see
.Xr zpool-import 8
for details on importing pools).
.
.Ss Unsupported features
For each unsupported feature enabled on an imported pool, a pool property
named
.Sy unsupported Ns @ Ns Ar feature-name
will indicate why the import was allowed despite the unsupported feature.
Possible values for this property are:
.Bl -tag -width "readonly"
.It Sy inactive
The feature is in the
.Sy enabled
state and therefore the pool's on-disk
format is still compatible with software that does not support this feature.
.It Sy readonly
The feature is read-only compatible and the pool has been imported in
read-only mode.
.El
.
.Ss Feature dependencies
Some features depend on other features being enabled in order to function.
Enabling a feature will automatically enable any features it depends on.
.
.Ss Compatibility feature sets
It is sometimes necessary for a pool to maintain compatibility with a
specific on-disk format, by enabling and disabling particular features.
The
.Sy compatibility
feature facilitates this by allowing feature sets to be read from text files.
When set to
.Sy off
(the default), compatibility feature sets are disabled
(i.e. all features are enabled); when set to
.Sy legacy ,
no features are enabled.
When set to a comma-separated list of filenames
(each filename may either be an absolute path, or relative to
.Pa /etc/zfs/compatibility.d
or
.Pa /usr/share/zfs/compatibility.d ) ,
the lists of requested features are read from those files,
separated by whitespace and/or commas.
Only features present in all files are enabled.
.Pp
Simple sanity checks are applied to the files:
they must be between 1B and 16kB in size, and must end with a newline character.
.Pp
The requested features are applied when a pool is created using
.Nm zpool Cm create Fl o Sy compatibility Ns = Ns Ar …
and controls which features are enabled when using
.Nm zpool Cm upgrade .
.Nm zpool Cm status
will not show a warning about disabled features which are not part
of the requested feature set.
.Pp
The special value
.Sy legacy
prevents any features from being enabled, either via
.Nm zpool Cm upgrade
or
.Nm zpool Cm set Sy feature Ns @ Ns Ar feature-name Ns = Ns Sy enabled .
This setting also prevents pools from being upgraded to newer on-disk versions.
This is a safety measure to prevent new features from being
accidentally enabled, breaking compatibility.
.Pp
By convention, compatibility files in
.Pa /usr/share/zfs/compatibility.d
are provided by the distribution, and include feature sets
supported by important versions of popular distributions, and feature
sets commonly supported at the start of each year.
Compatibility files in
.Pa /etc/zfs/compatibility.d ,
if present, will take precedence over files with the same name in
.Pa /usr/share/zfs/compatibility.d .
.Pp
If an unrecognized feature is found in these files, an error message will
be shown.
If the unrecognized feature is in a file in
.Pa /etc/zfs/compatibility.d ,
this is treated as an error and processing will stop.
If the unrecognized feature is under
.Pa /usr/share/zfs/compatibility.d ,
this is treated as a warning and processing will continue.
This difference is to allow distributions to include features
which might not be recognized by the currently-installed binaries.
.Pp
Compatibility files may include comments:
any text from
.Sq #
to the end of the line is ignored.
.Pp
.Sy Example :
.Bd -literal -compact -offset 4n
.No example# Nm cat Pa /usr/share/zfs/compatibility.d/grub2
# Features which are supported by GRUB2
async_destroy
bookmarks
embedded_data
empty_bpobj
enabled_txg
extensible_dataset
filesystem_limits
hole_birth
large_blocks
lz4_compress
spacemap_histogram
.No example# Nm zpool Cm create Fl o Sy compatibility Ns = Ns Ar grub2 Ar bootpool Ar vdev
.Ed
.Pp
See
.Xr zpool-create 8
and
.Xr zpool-upgrade 8
for more information on how these commands are affected by feature sets.
.
.de feature
.It Sy \\$2
.Bl -tag -compact -width "READ-ONLY COMPATIBLE"
.It GUID
.Sy \\$1:\\$2
.if !"\\$4"" \{\
.It DEPENDENCIES
\fB\\$4\fP\c
.if !"\\$5"" , \fB\\$5\fP\c
.if !"\\$6"" , \fB\\$6\fP\c
.if !"\\$7"" , \fB\\$7\fP\c
.if !"\\$8"" , \fB\\$8\fP\c
.if !"\\$9"" , \fB\\$9\fP\c
.\}
.It READ-ONLY COMPATIBLE
\\$3
.El
.Pp
..
.
.ds instant-never \
.No This feature becomes Sy active No as soon as it is enabled \
and will never return to being Sy enabled .
.
.ds remount-upgrade \
.No Each filesystem will be upgraded automatically when remounted, \
or when a new file is created under that filesystem. \
The upgrade can also be triggered on filesystems via \
Nm zfs Cm set Sy version Ns = Ns Sy current Ar fs . \
No The upgrade process runs in the background and may take a while to complete \
for filesystems containing large amounts of files.
.
.de checksum-spiel
When the
.Sy \\$1
feature is set to
.Sy enabled ,
the administrator can turn on the
.Sy \\$1
checksum on any dataset using
.Nm zfs Cm set Sy checksum Ns = Ns Sy \\$1 Ar dset
.Po see Xr zfs-set 8 Pc .
This feature becomes
.Sy active
once a
.Sy checksum
property has been set to
.Sy \\$1 ,
and will return to being
.Sy enabled
once all filesystems that have ever had their checksum set to
.Sy \\$1
are destroyed.
..
.
.Sh FEATURES
The following features are supported on this system:
.Bl -tag -width Ds
.feature org.zfsonlinux allocation_classes yes
This feature enables support for separate allocation classes.
.Pp
This feature becomes
.Sy active
when a dedicated allocation class vdev (dedup or special) is created with the
.Nm zpool Cm create No or Nm zpool Cm add No commands .
With device removal, it can be returned to the
.Sy enabled
state if all the dedicated allocation class vdevs are removed.
.
.feature com.delphix async_destroy yes
Destroying a file system requires traversing all of its data in order to
return its used space to the pool.
Without
.Sy async_destroy ,
the file system is not fully removed until all space has been reclaimed.
If the destroy operation is interrupted by a reboot or power outage,
the next attempt to open the pool will need to complete the destroy
operation synchronously.
.Pp
When
.Sy async_destroy
is enabled, the file system's data will be reclaimed by a background process,
allowing the destroy operation to complete
without traversing the entire file system.
The background process is able to resume
interrupted destroys after the pool has been opened, eliminating the need
to finish interrupted destroys as part of the open operation.
The amount of space remaining to be reclaimed by the background process
is available through the
.Sy freeing
property.
.Pp
This feature is only
.Sy active
while
.Sy freeing
is non-zero.
.
.feature com.delphix bookmarks yes extensible_dataset
This feature enables use of the
.Nm zfs Cm bookmark
command.
.Pp
This feature is
.Sy active
while any bookmarks exist in the pool.
All bookmarks in the pool can be listed by running
.Nm zfs Cm list Fl t Sy bookmark Fl r Ar poolname .
.
.feature com.datto bookmark_v2 no bookmark extensible_dataset
This feature enables the creation and management of larger bookmarks which are
needed for other features in ZFS.
.Pp
This feature becomes
.Sy active
when a v2 bookmark is created and will be returned to the
.Sy enabled
state when all v2 bookmarks are destroyed.
.
.feature com.delphix bookmark_written no bookmark extensible_dataset bookmark_v2
This feature enables additional bookmark accounting fields, enabling the
.Sy written Ns # Ns Ar bookmark
property (space written since a bookmark) and estimates of
send stream sizes for incrementals from bookmarks.
.Pp
This feature becomes
.Sy active
when a bookmark is created and will be
returned to the
.Sy enabled
state when all bookmarks with these fields are destroyed.
.
.feature org.openzfs device_rebuild yes
This feature enables the ability for the
.Nm zpool Cm attach
and
.Nm zpool Cm replace
commands to perform sequential reconstruction
(instead of healing reconstruction) when resilvering.
.Pp
Sequential reconstruction resilvers a device in LBA order without immediately
verifying the checksums.
Once complete, a scrub is started, which then verifies the checksums.
This approach allows full redundancy to be restored to the pool
in the minimum amount of time.
This two-phase approach will take longer than a healing resilver
when the time to verify the checksums is included.
However, unless there is additional pool damage,
no checksum errors should be reported by the scrub.
This feature is incompatible with raidz configurations.
.
This feature becomes
.Sy active
while a sequential resilver is in progress, and returns to
.Sy enabled
when the resilver completes.
.
.feature com.delphix device_removal no
This feature enables the
.Nm zpool Cm remove
command to remove top-level vdevs,
evacuating them to reduce the total size of the pool.
.Pp
This feature becomes
.Sy active
when the
.Nm zpool Cm remove
command is used
on a top-level vdev, and will never return to being
.Sy enabled .
.
.feature org.openzfs draid no
This feature enables use of the
.Sy draid
vdev type.
dRAID is a variant of raidz which provides integrated distributed
hot spares that allow faster resilvering while retaining the benefits of raidz.
Data, parity, and spare space are organized in redundancy groups
and distributed evenly over all of the devices.
.Pp
This feature becomes
.Sy active
when creating a pool which uses the
.Sy draid
vdev type, or when adding a new
.Sy draid
vdev to an existing pool.
.
.feature org.illumos edonr no extensible_dataset
This feature enables the use of the Edon-R hash algorithm for checksum,
including for nopwrite (if compression is also enabled, an overwrite of
a block whose checksum matches the data being written will be ignored).
In an abundance of caution, Edon-R requires verification when used with
dedup:
.Nm zfs Cm set Sy dedup Ns = Ns Sy edonr , Ns Sy verify
.Po see Xr zfs-set 8 Pc .
.Pp
Edon-R is a very high-performance hash algorithm that was part
of the NIST SHA-3 competition.
It provides extremely high hash performance (over 350% faster than SHA-256),
but was not selected because of its unsuitability
as a general purpose secure hash algorithm.
This implementation utilizes the new salted checksumming functionality
in ZFS, which means that the checksum is pre-seeded with a secret
256-bit random key (stored on the pool) before being fed the data block
to be checksummed.
Thus the produced checksums are unique to a given pool,
preventing hash collision attacks on systems with dedup.
.Pp
.checksum-spiel edonr
.Pp
.Fx does not support the Sy edonr No feature.
.
.feature com.delphix embedded_data no
This feature improves the performance and compression ratio of
highly-compressible blocks.
Blocks whose contents can compress to 112 bytes
or smaller can take advantage of this feature.
.Pp
When this feature is enabled, the contents of highly-compressible blocks are
stored in the block "pointer" itself (a misnomer in this case, as it contains
the compressed data, rather than a pointer to its location on disk).
Thus the space of the block (one sector, typically 512B or 4kB) is saved,
and no additional I/O is needed to read and write the data block.
.
\*[instant-never]
.
.feature com.delphix empty_bpobj yes
This feature increases the performance of creating and using a large
number of snapshots of a single filesystem or volume, and also reduces
the disk space required.
.Pp
When there are many snapshots, each snapshot uses many Block Pointer
Objects (bpobjs) to track blocks associated with that snapshot.
However, in common use cases, most of these bpobjs are empty.
This feature allows us to create each bpobj on-demand,
thus eliminating the empty bpobjs.
.Pp
This feature is
.Sy active
while there are any filesystems, volumes,
or snapshots which were created after enabling this feature.
.
.feature com.delphix enabled_txg yes
Once this feature is enabled, ZFS records the transaction group number
in which new features are enabled.
This has no user-visible impact, but other features may depend on this feature.
.Pp
This feature becomes
.Sy active
as soon as it is enabled and will
never return to being
.Sy enabled .
.
.feature com.datto encryption no bookmark_v2 extensible_dataset
This feature enables the creation and management of natively encrypted datasets.
.Pp
This feature becomes
.Sy active
when an encrypted dataset is created and will be returned to the
.Sy enabled
state when all datasets that use this feature are destroyed.
.
.feature com.delphix extensible_dataset no
This feature allows more flexible use of internal ZFS data structures,
and exists for other features to depend on.
.Pp
This feature will be
.Sy active
when the first dependent feature uses it, and will be returned to the
.Sy enabled
state when all datasets that use this feature are destroyed.
.
.feature com.joyent filesystem_limits yes extensible_dataset
This feature enables filesystem and snapshot limits.
These limits can be used to control how many filesystems and/or snapshots
can be created at the point in the tree on which the limits are set.
.Pp
This feature is
.Sy active
once either of the limit properties has been set on a dataset.
Once activated the feature is never deactivated.
.
.feature com.delphix hole_birth no enabled_txg
This feature has/had bugs, the result of which is that, if you do a
.Nm zfs Cm send Fl i
.Pq or Fl R , No since it uses Fl i
from an affected dataset, the receiving party will not see any checksum
or other errors, but the resulting destination snapshot
will not match the source.
Its use by
.Nm zfs Cm send Fl i
has been disabled by default
.Pq see Sy send_holes_without_birth_time No in Xr zfs-module-parameters 5 .
.Pp
This feature improves performance of incremental sends
.Pq Nm zfs Cm send Fl i
and receives for objects with many holes.
The most common case of hole-filled objects is zvols.
.Pp
An incremental send stream from snapshot
.Sy A No to snapshot Sy B
contains information about every block that changed between
.Sy A No and Sy B .
Blocks which did not change between those snapshots can be
identified and omitted from the stream using a piece of metadata called
the "block birth time", but birth times are not recorded for holes
(blocks filled only with zeroes).
Since holes created after
.Sy A No cannot be distinguished from holes created before Sy A ,
information about every hole in the entire filesystem or zvol
is included in the send stream.
.Pp
For workloads where holes are rare this is not a problem.
However, when incrementally replicating filesystems or zvols with many holes
(for example a zvol formatted with another filesystem) a lot of time will
be spent sending and receiving unnecessary information about holes that
already exist on the receiving side.
.Pp
Once the
.Sy hole_birth
feature has been enabled the block birth times
of all new holes will be recorded.
Incremental sends between snapshots created after this feature is enabled
will use this new metadata to avoid sending information about holes that
already exist on the receiving side.
.Pp
\*[instant-never]
.
.feature org.open-zfs large_blocks no extensible_dataset
This feature allows the record size on a dataset to be set larger than 128kB.
.Pp
This feature becomes
.Sy active
once a dataset contains a file with a block size larger than 128kB,
and will return to being
.Sy enabled
once all filesystems that have ever had their recordsize larger than 128kB
are destroyed.
.
.feature org.zfsonlinux large_dnode no extensible_dataset
This feature allows the size of dnodes in a dataset to be set larger than 512B.
.
This feature becomes
.Sy active
once a dataset contains an object with a dnode larger than 512B,
which occurs as a result of setting the
.Sy dnodesize
dataset property to a value other than
.Sy legacy .
The feature will return to being
.Sy enabled
once all filesystems that have ever contained a dnode larger than 512B
are destroyed.
Large dnodes allow more data to be stored in the bonus buffer,
thus potentially improving performance by avoiding the use of spill blocks.
.
.feature com.delphix livelist yes
This feature allows clones to be deleted faster than the traditional method
when a large number of random/sparse writes have been made to the clone.
All blocks allocated and freed after a clone is created are tracked by the
the clone's livelist which is referenced during the deletion of the clone.
The feature is activated when a clone is created and remains
.Sy active
until all clones have been destroyed.
.
.feature com.delphix log_spacemap yes com.delphix:spacemap_v2
This feature improves performance for heavily-fragmented pools,
especially when workloads are heavy in random-writes.
It does so by logging all the metaslab changes on a single spacemap every TXG
instead of scattering multiple writes to all the metaslab spacemaps.
.Pp
\*[instant-never]
.
.feature org.illumos lz4_compress no
.Sy lz4
is a high-performance real-time compression algorithm that
features significantly faster compression and decompression as well as a
higher compression ratio than the older
.Sy lzjb
compression.
Typically,
.Sy lz4
compression is approximately 50% faster on compressible data and 200% faster
on incompressible data than
.Sy lzjb .
It is also approximately 80% faster on decompression,
while giving approximately a 10% better compression ratio.
.Pp
When the
.Sy lz4_compress
feature is set to
.Sy enabled ,
the administrator can turn on
.Sy lz4
compression on any dataset on the pool using the
.Xr zfs-set 8
command.
All newly written metadata will be compressed with the
.Sy lz4
algorithm.
.Pp
\*[instant-never]
.
.feature com.joyent multi_vdev_crash_dump no
This feature allows a dump device to be configured with a pool comprised
of multiple vdevs.
Those vdevs may be arranged in any mirrored or raidz configuration.
.Pp
When the
.Sy multi_vdev_crash_dump
feature is set to
.Sy enabled ,
the administrator can use
.Xr dumpadm 1M
to configure a dump device on a pool comprised of multiple vdevs.
.Pp
Under
.Fx
and Linux this feature is unused, but registered for compatibility.
New pools created on these systems will have the feature
.Sy enabled
but will never transition to
.Sy active ,
as this functionality is not required for crash dump support.
Existing pools where this feature is
.Sy active
can be imported.
.
.feature com.delphix obsolete_counts yes device_removal
This feature is an enhancement of
.Sy device_removal ,
which will over time reduce the memory used to track removed devices.
When indirect blocks are freed or remapped,
we note that their part of the indirect mapping is "obsolete" – no longer needed.
.Pp
This feature becomes
.Sy active
when the
.Nm zpool Cm remove
command is used on a top-level vdev, and will never return to being
.Sy enabled .
.
.feature org.zfsonlinux project_quota yes extensible_dataset
This feature allows administrators to account the spaces and objects usage
information against the project identifier (ID).
.Pp
The project ID is an object-based attribute.
When upgrading an existing filesystem,
objects without a project ID will be assigned a zero project ID.
When this feature is enabled, newly created objects inherit
their parent directories' project ID if the parent's inherit flag is set
.Pq via Nm chattr Sy [+-]P No or Nm zfs Cm project Fl s Ns | Ns Fl C .
Otherwise, the new object's project ID will be zero.
An object's project ID can be changed at any time by the owner
(or privileged user) via
.Nm chattr Fl p Ar prjid
or
.Nm zfs Cm project Fl p Ar prjid .
.Pp
This feature will become
.Sy active
as soon as it is enabled and will never return to being
.Sy disabled .
\*[remount-upgrade]
.
.feature com.delphix redaction_bookmarks no bookmarks extensible_dataset
This feature enables the use of redacted
.Nm zfs Cm send Ns s ,
which create redaction bookmarks storing the list of blocks
redacted by the send that created them.
For more information about redacted sends, see
.Xr zfs-send 8 .
.
.feature com.delphix redacted_datasets no extensible_dataset
This feature enables the receiving of redacted
.Nm zfs Cm send Ns
streams. which create redacted datasets when received.
These datasets are missing some of their blocks,
and so cannot be safely mounted, and their contents cannot be safely read.
For more information about redacted receives, see
.Xr zfs-send 8 .
.
.feature com.datto resilver_defer yes
This feature allows ZFS to postpone new resilvers if an existing one is already
in progress.
Without this feature, any new resilvers will cause the currently
running one to be immediately restarted from the beginning.
.Pp
This feature becomes
.Sy active
once a resilver has been deferred, and returns to being
.Sy enabled
when the deferred resilver begins.
.
.feature org.illumos sha512 no extensible_dataset
This feature enables the use of the SHA-512/256 truncated hash algorithm
(FIPS 180-4) for checksum and dedup.
The native 64-bit arithmetic of SHA-512 provides an approximate 50%
performance boost over SHA-256 on 64-bit hardware
and is thus a good minimum-change replacement candidate
for systems where hash performance is important,
but these systems cannot for whatever reason utilize the faster
.Sy skein No and Sy edonr
algorithms.
.Pp
.checksum-spiel sha512
.
.feature org.illumos skein no extensible_dataset
This feature enables the use of the Skein hash algorithm for checksum and dedup.
Skein is a high-performance secure hash algorithm that was a
finalist in the NIST SHA-3 competition.
It provides a very high security margin and high performance on 64-bit hardware
(80% faster than SHA-256).
This implementation also utilizes the new salted checksumming
functionality in ZFS, which means that the checksum is pre-seeded with a
secret 256-bit random key (stored on the pool) before being fed the data
block to be checksummed.
Thus the produced checksums are unique to a given pool,
preventing hash collision attacks on systems with dedup.
.Pp
.checksum-spiel skein
.
.feature com.delphix spacemap_histogram yes
This features allows ZFS to maintain more information about how free space
is organized within the pool.
If this feature is
.Sy enabled ,
it will be activated when a new space map object is created, or
an existing space map is upgraded to the new format,
and never returns back to being
.Sy enabled .
.
.feature com.delphix spacemap_v2 yes
This feature enables the use of the new space map encoding which
consists of two words (instead of one) whenever it is advantageous.
The new encoding allows space maps to represent large regions of
space more efficiently on-disk while also increasing their maximum
addressable offset.
.Pp
This feature becomes
.Sy active
once it is
.Sy enabled ,
and never returns back to being
.Sy enabled .
.
.feature org.zfsonlinux userobj_accounting yes extensible_dataset
This feature allows administrators to account the object usage information
by user and group.
.Pp
\*[instant-never]
\*[remount-upgrade]
.
.feature com.delphix zpool_checkpoint yes
This feature enables the
.Nm zpool Cm checkpoint
command that can checkpoint the state of the pool
at the time it was issued and later rewind back to it or discard it.
.Pp
This feature becomes
.Sy active
when the
.Nm zpool Cm checkpoint
command is used to checkpoint the pool.
The feature will only return back to being
.Sy enabled
when the pool is rewound or the checkpoint has been discarded.
.
.feature org.freebsd zstd_compress no extensible_dataset
.Sy zstd
is a high-performance compression algorithm that features a
combination of high compression ratios and high speed.
Compared to
.Sy gzip ,
.Sy zstd
offers slightly better compression at much higher speeds.
Compared to
.Sy lz4 ,
.Sy zstd
offers much better compression while being only modestly slower.
Typically,
.Sy zstd
compression speed ranges from 250 to 500 MB/s per thread
and decompression speed is over 1 GB/s per thread.
.Pp
When the
.Sy zstd
feature is set to
.Sy enabled ,
the administrator can turn on
.Sy zstd
compression of any dataset using
.Nm zfs Cm set Sy compress Ns = Ns Sy zstd Ar dset
.Po see Xr zfs-set 8 Pc .
This feature becomes
.Sy active
once a
.Sy compress
property has been set to
.Sy zstd ,
and will return to being
.Sy enabled
once all filesystems that have ever had their
.Sy compress
property set to
.Sy zstd
are destroyed.
.El
.
.Sh SEE ALSO
.Xr zpool 8