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.\"
.\" CDDL HEADER START
.\"
.\" 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]
.\"
.\" CDDL HEADER END
.\"
.\"
.\" Copyright (c) 2007, Sun Microsystems, Inc. All Rights Reserved.
.\" Copyright (c) 2012, 2018 by Delphix. All rights reserved.
.\" Copyright (c) 2012 Cyril Plisko. All Rights Reserved.
.\" Copyright (c) 2017 Datto Inc.
.\" Copyright (c) 2018 George Melikov. All Rights Reserved.
.\" Copyright 2017 Nexenta Systems, Inc.
.\" Copyright (c) 2017 Open-E, Inc. All Rights Reserved.
.\"
.Dd November 29, 2018
.Dt ZPOOL 8 SMM
.Os Linux
.Sh NAME
.Nm zpool
.Nd configure ZFS storage pools
.Sh SYNOPSIS
.Nm
.Fl ?
.Nm
.Cm add
.Op Fl fgLnP
.Oo Fl o Ar property Ns = Ns Ar value Oc
.Ar pool vdev Ns ...
.Nm
.Cm attach
.Op Fl f
.Oo Fl o Ar property Ns = Ns Ar value Oc
.Ar pool device new_device
.Nm
.Cm checkpoint
.Op Fl d, -discard
.Ar pool
.Nm
.Cm clear
.Ar pool
.Op Ar device
.Nm
.Cm create
.Op Fl dfn
.Op Fl m Ar mountpoint
.Oo Fl o Ar property Ns = Ns Ar value Oc Ns ...
.Oo Fl o Ar feature@feature Ns = Ns Ar value Oc
.Oo Fl O Ar file-system-property Ns = Ns Ar value Oc Ns ...
.Op Fl R Ar root
.Ar pool vdev Ns ...
.Nm
.Cm destroy
.Op Fl f
.Ar pool
.Nm
.Cm detach
.Ar pool device
.Nm
.Cm events
.Op Fl vHf Oo Ar pool Oc | Fl c
.Nm
.Cm export
.Op Fl a
.Op Fl f
.Ar pool Ns ...
.Nm
.Cm get
.Op Fl Hp
.Op Fl o Ar field Ns Oo , Ns Ar field Oc Ns ...
.Sy all Ns | Ns Ar property Ns Oo , Ns Ar property Oc Ns ...
.Oo Ar pool Oc Ns ...
.Nm
.Cm history
.Op Fl il
.Oo Ar pool Oc Ns ...
.Nm
.Cm import
.Op Fl D
.Op Fl d Ar dir Ns | Ns device
.Nm
.Cm import
.Fl a
.Op Fl DflmN
.Op Fl F Oo Fl n Oc Oo Fl T Oc Oo Fl X Oc
.Op Fl -rewind-to-checkpoint
.Op Fl c Ar cachefile Ns | Ns Fl d Ar dir Ns | Ns device
.Op Fl o Ar mntopts
.Oo Fl o Ar property Ns = Ns Ar value Oc Ns ...
.Op Fl R Ar root
.Nm
.Cm import
.Op Fl Dflm
.Op Fl F Oo Fl n Oc Oo Fl T Oc Oo Fl X Oc
.Op Fl -rewind-to-checkpoint
.Op Fl c Ar cachefile Ns | Ns Fl d Ar dir Ns | Ns device
.Op Fl o Ar mntopts
.Oo Fl o Ar property Ns = Ns Ar value Oc Ns ...
.Op Fl R Ar root
.Op Fl s
.Ar pool Ns | Ns Ar id
.Op Ar newpool Oo Fl t Oc
.Nm
.Cm initialize
.Op Fl c | Fl s
.Ar pool
.Op Ar device Ns ...
.Nm
.Cm iostat
.Op Oo Oo Fl c Ar SCRIPT Oc Oo Fl lq Oc Oc Ns | Ns Fl rw
.Op Fl T Sy u Ns | Ns Sy d
.Op Fl ghHLnpPvy
.Oo Oo Ar pool Ns ... Oc Ns | Ns Oo Ar pool vdev Ns ... Oc Ns | Ns Oo Ar vdev Ns ... Oc Oc
.Op Ar interval Op Ar count
.Nm
.Cm labelclear
.Op Fl f
.Ar device
.Nm
.Cm list
.Op Fl HgLpPv
.Op Fl o Ar property Ns Oo , Ns Ar property Oc Ns ...
.Op Fl T Sy u Ns | Ns Sy d
.Oo Ar pool Oc Ns ...
.Op Ar interval Op Ar count
.Nm
.Cm offline
.Op Fl f
.Op Fl t
.Ar pool Ar device Ns ...
.Nm
.Cm online
.Op Fl e
.Ar pool Ar device Ns ...
.Nm
.Cm reguid
.Ar pool
.Nm
.Cm reopen
.Op Fl n
.Ar pool
.Nm
.Cm remove
.Op Fl np
.Ar pool Ar device Ns ...
.Nm
.Cm remove
.Fl s
.Ar pool
.Nm
.Cm replace
.Op Fl f
.Oo Fl o Ar property Ns = Ns Ar value Oc
.Ar pool Ar device Op Ar new_device
.Nm
.Cm resilver
.Ar pool Ns ...
.Nm
.Cm scrub
.Op Fl s | Fl p
.Ar pool Ns ...
.Nm
.Cm trim
.Op Fl d
.Op Fl r Ar rate
.Op Fl c | Fl s
.Ar pool
.Op Ar device Ns ...
.Nm
.Cm set
.Ar property Ns = Ns Ar value
.Ar pool
.Nm
.Cm split
.Op Fl gLlnP
.Oo Fl o Ar property Ns = Ns Ar value Oc Ns ...
.Op Fl R Ar root
.Ar pool newpool
.Oo Ar device Oc Ns ...
.Nm
.Cm status
.Oo Fl c Ar SCRIPT Oc
.Op Fl DigLpPstvx
.Op Fl T Sy u Ns | Ns Sy d
.Oo Ar pool Oc Ns ...
.Op Ar interval Op Ar count
.Nm
.Cm sync
.Oo Ar pool Oc Ns ...
.Nm
.Cm upgrade
.Nm
.Cm upgrade
.Fl v
.Nm
.Cm upgrade
.Op Fl V Ar version
.Fl a Ns | Ns Ar pool Ns ...
.Sh DESCRIPTION
The
.Nm
command configures ZFS storage pools.
A storage pool is a collection of devices that provides physical storage and
data replication for ZFS datasets.
All datasets within a storage pool share the same space.
See
.Xr zfs 8
for information on managing datasets.
.Ss Virtual Devices (vdevs)
A "virtual device" describes a single device or a collection of devices
organized according to certain performance and fault characteristics.
The following virtual devices are supported:
.Bl -tag -width Ds
.It Sy disk
A block device, typically located under
.Pa /dev .
ZFS can use individual slices or partitions, though the recommended mode of
operation is to use whole disks.
A disk can be specified by a full path, or it can be a shorthand name
.Po the relative portion of the path under
.Pa /dev
.Pc .
A whole disk can be specified by omitting the slice or partition designation.
For example,
.Pa sda
is equivalent to
.Pa /dev/sda .
When given a whole disk, ZFS automatically labels the disk, if necessary.
.It Sy file
A regular file.
The use of files as a backing store is strongly discouraged.
It is designed primarily for experimental purposes, as the fault tolerance of a
file is only as good as the file system of which it is a part.
A file must be specified by a full path.
.It Sy mirror
A mirror of two or more devices.
Data is replicated in an identical fashion across all components of a mirror.
A mirror with N disks of size X can hold X bytes and can withstand (N-1) devices
failing before data integrity is compromised.
.It Sy raidz , raidz1 , raidz2 , raidz3
A variation on RAID-5 that allows for better distribution of parity and
eliminates the RAID-5
.Qq write hole
.Pq in which data and parity become inconsistent after a power loss .
Data and parity is striped across all disks within a raidz group.
.Pp
A raidz group can have single-, double-, or triple-parity, meaning that the
raidz group can sustain one, two, or three failures, respectively, without
losing any data.
The
.Sy raidz1
vdev type specifies a single-parity raidz group; the
.Sy raidz2
vdev type specifies a double-parity raidz group; and the
.Sy raidz3
vdev type specifies a triple-parity raidz group.
The
.Sy raidz
vdev type is an alias for
.Sy raidz1 .
.Pp
A raidz group with N disks of size X with P parity disks can hold approximately
(N-P)*X bytes and can withstand P device(s) failing before data integrity is
compromised.
The minimum number of devices in a raidz group is one more than the number of
parity disks.
The recommended number is between 3 and 9 to help increase performance.
.It Sy spare
A special pseudo-vdev which keeps track of available hot spares for a pool.
For more information, see the
.Sx Hot Spares
section.
.It Sy log
A separate intent log device.
If more than one log device is specified, then writes are load-balanced between
devices.
Log devices can be mirrored.
However, raidz vdev types are not supported for the intent log.
For more information, see the
.Sx Intent Log
section.
.It Sy dedup
A device dedicated solely for allocating dedup data.
The redundancy of this device should match the redundancy of the other normal
devices in the pool. If more than one dedup device is specified, then
allocations are load-balanced between devices.
.It Sy special
A device dedicated solely for allocating various kinds of internal metadata,
and optionally small file data.
The redundancy of this device should match the redundancy of the other normal
devices in the pool. If more than one special device is specified, then
allocations are load-balanced between devices.
.Pp
For more information on special allocations, see the
.Sx Special Allocation Class
section.
.It Sy cache
A device used to cache storage pool data.
A cache device cannot be configured as a mirror or raidz group.
For more information, see the
.Sx Cache Devices
section.
.El
.Pp
Virtual devices cannot be nested, so a mirror or raidz virtual device can only
contain files or disks.
Mirrors of mirrors
.Pq or other combinations
are not allowed.
.Pp
A pool can have any number of virtual devices at the top of the configuration
.Po known as
.Qq root vdevs
.Pc .
Data is dynamically distributed across all top-level devices to balance data
among devices.
As new virtual devices are added, ZFS automatically places data on the newly
available devices.
.Pp
Virtual devices are specified one at a time on the command line, separated by
whitespace.
The keywords
.Sy mirror
and
.Sy raidz
are used to distinguish where a group ends and another begins.
For example, the following creates two root vdevs, each a mirror of two disks:
.Bd -literal
# zpool create mypool mirror sda sdb mirror sdc sdd
.Ed
.Ss Device Failure and Recovery
ZFS supports a rich set of mechanisms for handling device failure and data
corruption.
All metadata and data is checksummed, and ZFS automatically repairs bad data
from a good copy when corruption is detected.
.Pp
In order to take advantage of these features, a pool must make use of some form
of redundancy, using either mirrored or raidz groups.
While ZFS supports running in a non-redundant configuration, where each root
vdev is simply a disk or file, this is strongly discouraged.
A single case of bit corruption can render some or all of your data unavailable.
.Pp
A pool's health status is described by one of three states: online, degraded,
or faulted.
An online pool has all devices operating normally.
A degraded pool is one in which one or more devices have failed, but the data is
still available due to a redundant configuration.
A faulted pool has corrupted metadata, or one or more faulted devices, and
insufficient replicas to continue functioning.
.Pp
The health of the top-level vdev, such as mirror or raidz device, is
potentially impacted by the state of its associated vdevs, or component
devices.
A top-level vdev or component device is in one of the following states:
.Bl -tag -width "DEGRADED"
.It Sy DEGRADED
One or more top-level vdevs is in the degraded state because one or more
component devices are offline.
Sufficient replicas exist to continue functioning.
.Pp
One or more component devices is in the degraded or faulted state, but
sufficient replicas exist to continue functioning.
The underlying conditions are as follows:
.Bl -bullet
.It
The number of checksum errors exceeds acceptable levels and the device is
degraded as an indication that something may be wrong.
ZFS continues to use the device as necessary.
.It
The number of I/O errors exceeds acceptable levels.
The device could not be marked as faulted because there are insufficient
replicas to continue functioning.
.El
.It Sy FAULTED
One or more top-level vdevs is in the faulted state because one or more
component devices are offline.
Insufficient replicas exist to continue functioning.
.Pp
One or more component devices is in the faulted state, and insufficient
replicas exist to continue functioning.
The underlying conditions are as follows:
.Bl -bullet
.It
The device could be opened, but the contents did not match expected values.
.It
The number of I/O errors exceeds acceptable levels and the device is faulted to
prevent further use of the device.
.El
.It Sy OFFLINE
The device was explicitly taken offline by the
.Nm zpool Cm offline
command.
.It Sy ONLINE
The device is online and functioning.
.It Sy REMOVED
The device was physically removed while the system was running.
Device removal detection is hardware-dependent and may not be supported on all
platforms.
.It Sy UNAVAIL
The device could not be opened.
If a pool is imported when a device was unavailable, then the device will be
identified by a unique identifier instead of its path since the path was never
correct in the first place.
.El
.Pp
If a device is removed and later re-attached to the system, ZFS attempts
to put the device online automatically.
Device attach detection is hardware-dependent and might not be supported on all
platforms.
.Ss Hot Spares
ZFS allows devices to be associated with pools as
.Qq hot spares .
These devices are not actively used in the pool, but when an active device
fails, it is automatically replaced by a hot spare.
To create a pool with hot spares, specify a
.Sy spare
vdev with any number of devices.
For example,
.Bd -literal
# zpool create pool mirror sda sdb spare sdc sdd
.Ed
.Pp
Spares can be shared across multiple pools, and can be added with the
.Nm zpool Cm add
command and removed with the
.Nm zpool Cm remove
command.
Once a spare replacement is initiated, a new
.Sy spare
vdev is created within the configuration that will remain there until the
original device is replaced.
At this point, the hot spare becomes available again if another device fails.
.Pp
If a pool has a shared spare that is currently being used, the pool can not be
exported since other pools may use this shared spare, which may lead to
potential data corruption.
.Pp
Shared spares add some risk. If the pools are imported on different hosts, and
both pools suffer a device failure at the same time, both could attempt to use
the spare at the same time. This may not be detected, resulting in data
corruption.
.Pp
An in-progress spare replacement can be cancelled by detaching the hot spare.
If the original faulted device is detached, then the hot spare assumes its
place in the configuration, and is removed from the spare list of all active
pools.
.Pp
Spares cannot replace log devices.
.Ss Intent Log
The ZFS Intent Log (ZIL) satisfies POSIX requirements for synchronous
transactions.
For instance, databases often require their transactions to be on stable storage
devices when returning from a system call.
NFS and other applications can also use
.Xr fsync 2
to ensure data stability.
By default, the intent log is allocated from blocks within the main pool.
However, it might be possible to get better performance using separate intent
log devices such as NVRAM or a dedicated disk.
For example:
.Bd -literal
# zpool create pool sda sdb log sdc
.Ed
.Pp
Multiple log devices can also be specified, and they can be mirrored.
See the
.Sx EXAMPLES
section for an example of mirroring multiple log devices.
.Pp
Log devices can be added, replaced, attached, detached and removed. In
addition, log devices are imported and exported as part of the pool
that contains them.
Mirrored devices can be removed by specifying the top-level mirror vdev.
.Ss Cache Devices
Devices can be added to a storage pool as
.Qq cache devices .
These devices provide an additional layer of caching between main memory and
disk.
For read-heavy workloads, where the working set size is much larger than what
can be cached in main memory, using cache devices allow much more of this
working set to be served from low latency media.
Using cache devices provides the greatest performance improvement for random
read-workloads of mostly static content.
.Pp
To create a pool with cache devices, specify a
.Sy cache
vdev with any number of devices.
For example:
.Bd -literal
# zpool create pool sda sdb cache sdc sdd
.Ed
.Pp
Cache devices cannot be mirrored or part of a raidz configuration.
If a read error is encountered on a cache device, that read I/O is reissued to
the original storage pool device, which might be part of a mirrored or raidz
configuration.
.Pp
The content of the cache devices is considered volatile, as is the case with
other system caches.
.Ss Pool checkpoint
Before starting critical procedures that include destructive actions (e.g
.Nm zfs Cm destroy
), an administrator can checkpoint the pool's state and in the case of a
mistake or failure, rewind the entire pool back to the checkpoint.
Otherwise, the checkpoint can be discarded when the procedure has completed
successfully.
.Pp
A pool checkpoint can be thought of as a pool-wide snapshot and should be used
with care as it contains every part of the pool's state, from properties to vdev
configuration.
Thus, while a pool has a checkpoint certain operations are not allowed.
Specifically, vdev removal/attach/detach, mirror splitting, and
changing the pool's guid.
Adding a new vdev is supported but in the case of a rewind it will have to be
added again.
Finally, users of this feature should keep in mind that scrubs in a pool that
has a checkpoint do not repair checkpointed data.
.Pp
To create a checkpoint for a pool:
.Bd -literal
# zpool checkpoint pool
.Ed
.Pp
To later rewind to its checkpointed state, you need to first export it and
then rewind it during import:
.Bd -literal
# zpool export pool
# zpool import --rewind-to-checkpoint pool
.Ed
.Pp
To discard the checkpoint from a pool:
.Bd -literal
# zpool checkpoint -d pool
.Ed
.Pp
Dataset reservations (controlled by the
.Nm reservation
or
.Nm refreservation
zfs properties) may be unenforceable while a checkpoint exists, because the
checkpoint is allowed to consume the dataset's reservation.
Finally, data that is part of the checkpoint but has been freed in the
current state of the pool won't be scanned during a scrub.
.Ss Special Allocation Class
The allocations in the special class are dedicated to specific block types.
By default this includes all metadata, the indirect blocks of user data, and
any dedup data. The class can also be provisioned to accept a limited
percentage of small file data blocks.
.Pp
A pool must always have at least one general (non-specified) vdev before
other devices can be assigned to the special class. If the special class
becomes full, then allocations intended for it will spill back into the
normal class.
.Pp
Dedup data can be excluded from the special class by setting the
.Sy zfs_ddt_data_is_special
zfs module parameter to false (0).
.Pp
Inclusion of small file blocks in the special class is opt-in. Each dataset
can control the size of small file blocks allowed in the special class by
setting the
.Sy special_small_blocks
dataset property. It defaults to zero so you must opt-in by setting it to a
non-zero value. See
.Xr zfs 8
for more info on setting this property.
.Ss Properties
Each pool has several properties associated with it.
Some properties are read-only statistics while others are configurable and
change the behavior of the pool.
.Pp
The following are read-only properties:
.Bl -tag -width Ds
.It Cm allocated
Amount of storage used within the pool.
.It Sy capacity
Percentage of pool space used.
This property can also be referred to by its shortened column name,
.Sy cap .
.It Sy expandsize
Amount of uninitialized space within the pool or device that can be used to
increase the total capacity of the pool.
Uninitialized space consists of any space on an EFI labeled vdev which has not
been brought online
.Po e.g, using
.Nm zpool Cm online Fl e
.Pc .
This space occurs when a LUN is dynamically expanded.
.It Sy fragmentation
The amount of fragmentation in the pool.
.It Sy free
The amount of free space available in the pool.
.It Sy freeing
After a file system or snapshot is destroyed, the space it was using is
returned to the pool asynchronously.
.Sy freeing
is the amount of space remaining to be reclaimed.
Over time
.Sy freeing
will decrease while
.Sy free
increases.
.It Sy health
The current health of the pool.
Health can be one of
.Sy ONLINE , DEGRADED , FAULTED , OFFLINE, REMOVED , UNAVAIL .
.It Sy guid
A unique identifier for the pool.
.It Sy load_guid
A unique identifier for the pool.
Unlike the
.Sy guid
property, this identifier is generated every time we load the pool (e.g. does
not persist across imports/exports) and never changes while the pool is loaded
(even if a
.Sy reguid
operation takes place).
.It Sy size
Total size of the storage pool.
.It Sy unsupported@ Ns Em feature_guid
Information about unsupported features that are enabled on the pool.
See
.Xr zpool-features 5
for details.
.El
.Pp
The space usage properties report actual physical space available to the
storage pool.
The physical space can be different from the total amount of space that any
contained datasets can actually use.
The amount of space used in a raidz configuration depends on the characteristics
of the data being written.
In addition, ZFS reserves some space for internal accounting that the
.Xr zfs 8
command takes into account, but the
.Nm
command does not.
For non-full pools of a reasonable size, these effects should be invisible.
For small pools, or pools that are close to being completely full, these
discrepancies may become more noticeable.
.Pp
The following property can be set at creation time and import time:
.Bl -tag -width Ds
.It Sy altroot
Alternate root directory.
If set, this directory is prepended to any mount points within the pool.
This can be used when examining an unknown pool where the mount points cannot be
trusted, or in an alternate boot environment, where the typical paths are not
valid.
.Sy altroot
is not a persistent property.
It is valid only while the system is up.
Setting
.Sy altroot
defaults to using
.Sy cachefile Ns = Ns Sy none ,
though this may be overridden using an explicit setting.
.El
.Pp
The following property can be set only at import time:
.Bl -tag -width Ds
.It Sy readonly Ns = Ns Sy on Ns | Ns Sy off
If set to
.Sy on ,
the pool will be imported in read-only mode.
This property can also be referred to by its shortened column name,
.Sy rdonly .
.El
.Pp
The following properties can be set at creation time and import time, and later
changed with the
.Nm zpool Cm set
command:
.Bl -tag -width Ds
.It Sy ashift Ns = Ns Sy ashift
Pool sector size exponent, to the power of
.Sy 2
(internally referred to as
.Sy ashift
). Values from 9 to 16, inclusive, are valid; also, the special
value 0 (the default) means to auto-detect using the kernel's block
layer and a ZFS internal exception list. I/O operations will be aligned
to the specified size boundaries. Additionally, the minimum (disk)
write size will be set to the specified size, so this represents a
space vs. performance trade-off. For optimal performance, the pool
sector size should be greater than or equal to the sector size of the
underlying disks. The typical case for setting this property is when
performance is important and the underlying disks use 4KiB sectors but
report 512B sectors to the OS (for compatibility reasons); in that
case, set
.Sy ashift=12
(which is 1<<12 = 4096). When set, this property is
used as the default hint value in subsequent vdev operations (add,
attach and replace). Changing this value will not modify any existing
vdev, not even on disk replacement; however it can be used, for
instance, to replace a dying 512B sectors disk with a newer 4KiB
sectors device: this will probably result in bad performance but at the
same time could prevent loss of data.
.It Sy autoexpand Ns = Ns Sy on Ns | Ns Sy off
Controls automatic pool expansion when the underlying LUN is grown.
If set to
.Sy on ,
the pool will be resized according to the size of the expanded device.
If the device is part of a mirror or raidz then all devices within that
mirror/raidz group must be expanded before the new space is made available to
the pool.
The default behavior is
.Sy off .
This property can also be referred to by its shortened column name,
.Sy expand .
.It Sy autoreplace Ns = Ns Sy on Ns | Ns Sy off
Controls automatic device replacement.
If set to
.Sy off ,
device replacement must be initiated by the administrator by using the
.Nm zpool Cm replace
command.
If set to
.Sy on ,
any new device, found in the same physical location as a device that previously
belonged to the pool, is automatically formatted and replaced.
The default behavior is
.Sy off .
This property can also be referred to by its shortened column name,
.Sy replace .
Autoreplace can also be used with virtual disks (like device
mapper) provided that you use the /dev/disk/by-vdev paths setup by
vdev_id.conf. See the
.Xr vdev_id 8
man page for more details.
Autoreplace and autoonline require the ZFS Event Daemon be configured and
running. See the
.Xr zed 8
man page for more details.
.It Sy bootfs Ns = Ns Sy (unset) Ns | Ns Ar pool Ns / Ns Ar dataset
Identifies the default bootable dataset for the root pool. This property is
expected to be set mainly by the installation and upgrade programs.
Not all Linux distribution boot processes use the bootfs property.
.It Sy cachefile Ns = Ns Ar path Ns | Ns Sy none
Controls the location of where the pool configuration is cached.
Discovering all pools on system startup requires a cached copy of the
configuration data that is stored on the root file system.
All pools in this cache are automatically imported when the system boots.
Some environments, such as install and clustering, need to cache this
information in a different location so that pools are not automatically
imported.
Setting this property caches the pool configuration in a different location that
can later be imported with
.Nm zpool Cm import Fl c .
Setting it to the special value
.Sy none
creates a temporary pool that is never cached, and the special value
.Qq
.Pq empty string
uses the default location.
.Pp
Multiple pools can share the same cache file.
Because the kernel destroys and recreates this file when pools are added and
removed, care should be taken when attempting to access this file.
When the last pool using a
.Sy cachefile
is exported or destroyed, the file will be empty.
.It Sy comment Ns = Ns Ar text
A text string consisting of printable ASCII characters that will be stored
such that it is available even if the pool becomes faulted.
An administrator can provide additional information about a pool using this
property.
.It Sy dedupditto Ns = Ns Ar number
Threshold for the number of block ditto copies.
If the reference count for a deduplicated block increases above this number, a
new ditto copy of this block is automatically stored.
The default setting is
.Sy 0
which causes no ditto copies to be created for deduplicated blocks.
The minimum legal nonzero setting is
.Sy 100 .
.It Sy delegation Ns = Ns Sy on Ns | Ns Sy off
Controls whether a non-privileged user is granted access based on the dataset
permissions defined on the dataset.
See
.Xr zfs 8
for more information on ZFS delegated administration.
.It Sy failmode Ns = Ns Sy wait Ns | Ns Sy continue Ns | Ns Sy panic
Controls the system behavior in the event of catastrophic pool failure.
This condition is typically a result of a loss of connectivity to the underlying
storage device(s) or a failure of all devices within the pool.
The behavior of such an event is determined as follows:
.Bl -tag -width "continue"
.It Sy wait
Blocks all I/O access until the device connectivity is recovered and the errors
are cleared.
This is the default behavior.
.It Sy continue
Returns
.Er EIO
to any new write I/O requests but allows reads to any of the remaining healthy
devices.
Any write requests that have yet to be committed to disk would be blocked.
.It Sy panic
Prints out a message to the console and generates a system crash dump.
.El
.It Sy autotrim Ns = Ns Sy on Ns | Ns Sy off
When set to
.Sy on
space which has been recently freed, and is no longer allocated by the pool,
will be periodically trimmed. This allows block device vdevs which support
BLKDISCARD, such as SSDs, or file vdevs on which the underlying file system
supports hole-punching, to reclaim unused blocks. The default setting for
this property is
.Sy off .
.Pp
Automatic TRIM does not immediately reclaim blocks after a free. Instead,
it will optimistically delay allowing smaller ranges to be aggregated in to
a few larger ones. These can then be issued more efficiently to the storage.
.Pp
Be aware that automatic trimming of recently freed data blocks can put
significant stress on the underlying storage devices. This will vary
depending of how well the specific device handles these commands. For
lower end devices it is often possible to achieve most of the benefits
of automatic trimming by running an on-demand (manual) TRIM periodically
using the
.Nm zpool Cm trim
command.
.It Sy feature@ Ns Ar feature_name Ns = Ns Sy enabled
The value of this property is the current state of
.Ar feature_name .
The only valid value when setting this property is
.Sy enabled
which moves
.Ar feature_name
to the enabled state.
See
.Xr zpool-features 5
for details on feature states.
.It Sy listsnapshots Ns = Ns Sy on Ns | Ns Sy off
Controls whether information about snapshots associated with this pool is
output when
.Nm zfs Cm list
is run without the
.Fl t
option.
The default value is
.Sy off .
This property can also be referred to by its shortened name,
.Sy listsnaps .
.It Sy multihost Ns = Ns Sy on Ns | Ns Sy off
Controls whether a pool activity check should be performed during
.Nm zpool Cm import .
When a pool is determined to be active it cannot be imported, even with the
.Fl f
option. This property is intended to be used in failover configurations
where multiple hosts have access to a pool on shared storage.
Multihost provides protection on import only. It does not protect against an
individual device being used in multiple pools, regardless of the type of vdev.
See the discussion under
.Sy zpool create.
When this property is on, periodic writes to storage occur to show the pool is
in use. See
.Sy zfs_multihost_interval
in the
.Xr zfs-module-parameters 5
man page. In order to enable this property each host must set a unique hostid.
See
.Xr genhostid 1
.Xr zgenhostid 8
.Xr spl-module-parameters 5
for additional details. The default value is
.Sy off .
.It Sy version Ns = Ns Ar version
The current on-disk version of the pool.
This can be increased, but never decreased.
The preferred method of updating pools is with the
.Nm zpool Cm upgrade
command, though this property can be used when a specific version is needed for
backwards compatibility.
Once feature flags are enabled on a pool this property will no longer have a
value.
.El
.Ss Subcommands
All subcommands that modify state are logged persistently to the pool in their
original form.
.Pp
The
.Nm
command provides subcommands to create and destroy storage pools, add capacity
to storage pools, and provide information about the storage pools.
The following subcommands are supported:
.Bl -tag -width Ds
.It Xo
.Nm
.Fl ?
.Xc
Displays a help message.
.It Xo
.Nm
.Cm add
.Op Fl fgLnP
.Oo Fl o Ar property Ns = Ns Ar value Oc
.Ar pool vdev Ns ...
.Xc
Adds the specified virtual devices to the given pool.
The
.Ar vdev
specification is described in the
.Sx Virtual Devices
section.
The behavior of the
.Fl f
option, and the device checks performed are described in the
.Nm zpool Cm create
subcommand.
.Bl -tag -width Ds
.It Fl f
Forces use of
.Ar vdev Ns s ,
even if they appear in use or specify a conflicting replication level.
Not all devices can be overridden in this manner.
.It Fl g
Display
.Ar vdev ,
GUIDs instead of the normal device names. These GUIDs can be used in place of
device names for the zpool detach/offline/remove/replace commands.
.It Fl L
Display real paths for
.Ar vdev Ns s
resolving all symbolic links. This can be used to look up the current block
device name regardless of the /dev/disk/ path used to open it.
.It Fl n
Displays the configuration that would be used without actually adding the
.Ar vdev Ns s .
The actual pool creation can still fail due to insufficient privileges or
device sharing.
.It Fl P
Display real paths for
.Ar vdev Ns s
instead of only the last component of the path. This can be used in
conjunction with the
.Fl L
flag.
.It Fl o Ar property Ns = Ns Ar value
Sets the given pool properties. See the
.Sx Properties
section for a list of valid properties that can be set. The only property
supported at the moment is ashift.
.El
.It Xo
.Nm
.Cm attach
.Op Fl f
.Oo Fl o Ar property Ns = Ns Ar value Oc
.Ar pool device new_device
.Xc
Attaches
.Ar new_device
to the existing
.Ar device .
The existing device cannot be part of a raidz configuration.
If
.Ar device
is not currently part of a mirrored configuration,
.Ar device
automatically transforms into a two-way mirror of
.Ar device
and
.Ar new_device .
If
.Ar device
is part of a two-way mirror, attaching
.Ar new_device
creates a three-way mirror, and so on.
In either case,
.Ar new_device
begins to resilver immediately.
.Bl -tag -width Ds
.It Fl f
Forces use of
.Ar new_device ,
even if it appears to be in use.
Not all devices can be overridden in this manner.
.It Fl o Ar property Ns = Ns Ar value
Sets the given pool properties. See the
.Sx Properties
section for a list of valid properties that can be set. The only property
supported at the moment is ashift.