storage pools. A storage pool is a collection of devices that provides physical storage and data replication for
datasets.
All datasets within a storage pool share the same space. See zfs(1M) for information on managing datasets.
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:
disk
A block device, typically located under /dev/dsk. 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 (the relative portion of the path under "/dev/dsk"). A whole disk can be specified by omitting the slice or partition designation. For example, "c0t0d0" is equivalent to "/dev/dsk/c0t0d0s2". When given a whole disk, ZFS automatically labels the disk, if necessary.
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.
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.
raidz
raidz1
raidz2
raidz3
A variation on
RAID-5 that allows for better distribution of parity and eliminates the "
RAID-5 write hole" (in which data and parity become inconsistent after a power loss). Data and parity is striped across all disks within a
raidz group.
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
raidz1 vdev type specifies a single-parity
raidz group; the
raidz2 vdev type specifies a double-parity
raidz group; and the
raidz3 vdev type specifies a triple-parity
raidz group. The
raidz vdev type is an alias for
raidz1.
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.
spare
A special pseudo-vdev which keeps track of available hot spares for a pool. For more information, see the "Hot Spares" section.
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 "Intent Log" section.
cache
A device used to cache storage pool data. A cache device cannot be cannot be configured as a mirror or raidz group. For more information, see the "Cache Devices" section.
Virtual devices cannot be nested, so a mirror or raidz virtual device can only contain files or disks. Mirrors of mirrors (or other combinations) are not allowed.
A pool can have any number of virtual devices at the top of the configuration (known as "root vdevs"). 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.
Virtual devices are specified one at a time on the command line, separated by whitespace. The keywords "mirror" and "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:
#
zpool create mypool mirror c0t0d0 c0t1d0 mirror c1t0d0 c1t1d0
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. The following are read-only properties:
available
Amount of storage available within the pool. This property can also be referred to by its shortened column name, "avail".
capacity
Percentage of pool space used. This property can also be referred to by its shortened column name, "cap".
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 (i.e. zpool online -e). This space occurs when a LUN is dynamically expanded.
fragmentation
The amount of fragmentation in the pool.
free
The amount of free space available in the pool.
freeing
After a file system or snapshot is destroyed, the space it was using is returned to the pool asynchronously. freeing is the amount of space remaining to be reclaimed. Over time freeing will decrease while free increases.
health
The current health of the pool. Health can be "ONLINE", "DEGRADED", " FAULTED", " OFFLINE", "REMOVED", or "UNAVAIL".
guid
A unique identifier for the pool.
size
Total size of the storage pool.
unsupported@feature_guid
Information about unsupported features that are enabled on the pool. See zpool-features(5) for details.
used
Amount of storage space used within the pool.
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 zfs(1M) command takes into account, but the zpool 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.
The following property can be set at creation time and import time:
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. altroot is not a persistent property. It is valid only while the system is up. Setting altroot defaults to using cachefile=none, though this may be overridden using an explicit setting.
The following property can be set only at import time:
readonly=
on |
off
If set to on, the pool will be imported in read-only mode. This property can also be referred to by its shortened column name, rdonly.
The following properties can be set at creation time and import time, and later changed with the zpool set command:
autoexpand=
on |
off
Controls automatic pool expansion when the underlying LUN is grown. If set to 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 off. This property can also be referred to by its shortened column name, expand.
autoreplace=
on |
off
Controls automatic device replacement. If set to "off", device replacement must be initiated by the administrator by using the " zpool replace" command. If set to "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 " off". This property can also be referred to by its shortened column name, "replace".
bootfs=
pool/
dataset
Identifies the default bootable dataset for the root pool. This property is expected to be set mainly by the installation and upgrade programs.
cachefile=
path |
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 "
zpool import -c". Setting it to the special value "
none" creates a temporary pool that is never cached, and the special value
'' (empty string) uses the default location.
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
cachefile is exported or destroyed, the file is removed.
comment=
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.
dedupditto=
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 0 which causes no ditto copies to be created for deduplicated blocks. The miniumum legal nonzero setting is 100.
delegation=
on |
off
Controls whether a non-privileged user is granted access based on the dataset permissions defined on the dataset. See zfs(1M) for more information on ZFS delegated administration.
failmode=
wait |
continue |
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:
wait
Blocks all I/O access until the device connectivity is recovered and the errors are cleared. This is the default behavior.
continue
Returns 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.
panic
Prints out a message to the console and generates a system crash dump.
feature@feature_name=
enabled
The value of this property is the current state of feature_name. The only valid value when setting this property is enabled which moves feature_name to the enabled state. See zpool-features(5) for details on feature states.
listsnaps=on | off
Controls whether information about snapshots associated with this pool is output when " zfs list" is run without the -t option. The default value is "off".
version=
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 " zpool upgrade" command, though this property can be used when a specific version is needed for backwards compatibility. Once feature flags is enabled on a pool this property will no longer have a value.
Subcommands
All subcommands that modify state are logged persistently to the pool in their original form.
The zpool 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:
zpool -?
Displays a help message.
zpool add [
-fn]
pool vdev ...
Adds the specified virtual devices to the given pool. The
vdev specification is described in the "Virtual Devices" section. The behavior of the
-f option, and the device checks performed are described in the "zpool create" subcommand.
-f
Forces use of vdevs, even if they appear in use or specify a conflicting replication level. Not all devices can be overridden in this manner.
-n
Displays the configuration that would be used without actually adding the vdevs. The actual pool creation can still fail due to insufficient privileges or device sharing.
Do not add a disk that is currently configured as a quorum device to a zpool. After a disk is in the pool, that disk can then be configured as a quorum device.
zpool attach [
-f]
pool device new_device
Attaches
new_device to an existing
zpool device. The existing device cannot be part of a
raidz configuration. If
device is not currently part of a mirrored configuration,
device automatically transforms into a two-way mirror of
device and
new_device. If
device is part of a two-way mirror, attaching
new_device creates a three-way mirror, and so on. In either case,
new_device begins to resilver immediately.
-f
Forces use of new_device, even if its appears to be in use. Not all devices can be overridden in this manner.
zpool clear pool [
device] ...
Clears device errors in a pool. If no arguments are specified, all device errors within the pool are cleared. If one or more devices is specified, only those errors associated with the specified device or devices are cleared.
zpool create [
-fnd] [
-o property=value] ... [
-O file-system-property=value] ... [
-m mountpoint] [
-R root]
pool vdev ...
Creates a new storage pool containing the virtual devices specified on the command line. The pool name must begin with a letter, and can only contain alphanumeric characters as well as underscore ("_"), dash ("-"), and period ("."). The pool names "mirror", "raidz", "spare" and "log" are reserved, as are names beginning with the pattern "c[0-9]". The
vdev specification is described in the "Virtual Devices" section.
The command verifies that each device specified is accessible and not currently in use by another subsystem. There are some uses, such as being currently mounted, or specified as the dedicated dump device, that prevents a device from ever being used by
ZFS. Other uses, such as having a preexisting
UFS file system, can be overridden with the
-f option.
The command also checks that the replication strategy for the pool is consistent. An attempt to combine redundant and non-redundant storage in a single pool, or to mix disks and files, results in an error unless
-f is specified. The use of differently sized devices within a single
raidz or mirror group is also flagged as an error unless
-f is specified.
Unless the
-R option is specified, the default mount point is "/
pool". The mount point must not exist or must be empty, or else the root dataset cannot be mounted. This can be overridden with the
-m option.
By default all supported features are enabled on the new pool unless the
-d option is specified.
-f
Forces use of vdevs, even if they appear in use or specify a conflicting replication level. Not all devices can be overridden in this manner.
-n
Displays the configuration that would be used without actually creating the pool. The actual pool creation can still fail due to insufficient privileges or device sharing.
-d
Do not enable any features on the new pool. Individual features can be enabled by setting their corresponding properties to enabled with the -o option. See zpool-features(5) for details about feature properties.
-o property=value [
-o property=value] ...
Sets the given pool properties. See the "Properties" section for a list of valid properties that can be set.
-O file-system-property=value
[-O file-system-property=value] ...
Sets the given file system properties in the root file system of the pool. See the "Properties" section of zfs(1M) for a list of valid properties that can be set.
-R root
Equivalent to "-o cachefile=none,altroot=root"
-m mountpoint
Sets the mount point for the root dataset. The default mount point is "/ pool" or "altroot/pool" if altroot is specified. The mount point must be an absolute path, " legacy", or "none". For more information on dataset mount points, see zfs(1M).
zpool destroy [
-f]
pool
Destroys the given pool, freeing up any devices for other use. This command tries to unmount any active datasets before destroying the pool.
-f
Forces any active datasets contained within the pool to be unmounted.
zpool detach pool device
Detaches device from a mirror. The operation is refused if there are no other valid replicas of the data.
zpool export [
-f]
pool ...
Exports the given pools from the system. All devices are marked as exported, but are still considered in use by other subsystems. The devices can be moved between systems (even those of different endianness) and imported as long as a sufficient number of devices are present.
Before exporting the pool, all datasets within the pool are unmounted. A pool can not be exported if it has a shared spare that is currently being used.
For pools to be portable, you must give the
zpool command whole disks, not just slices, so that
ZFS can label the disks with portable
EFI labels. Otherwise, disk drivers on platforms of different endianness will not recognize the disks.
-f
Forcefully unmount all datasets, using the "
unmount -f" command.
This command will forcefully export the pool even if it has a shared spare that is currently being used. This may lead to potential data corruption.
zpool get [
-Hp] [
-o field[,...]] "
all" |
property[,...]
pool ...
Retrieves the given list of properties (or all properties if "
all" is used) for the specified storage pool(s). These properties are displayed with the following fields:
name Name of storage pool
property Property name
value Property value
source Property source, either 'default' or 'local'.
See the "Properties" section for more information on the available pool properties.
-H
Scripted mode. Do not display headers, and separate fields by a single tab instead of arbitrary space.
-p
Display numbers in parsable (exact) values.
-o field
A comma-separated list of columns to display. name,property,value,source is the default value.
zpool history [
-il] [
pool] ...
Displays the command history of the specified pools or all pools if no pool is specified.
-i
Displays internally logged ZFS events in addition to user initiated events.
-l
Displays log records in long format, which in addition to standard format includes, the user name, the hostname, and the zone in which the operation was performed.
zpool import [
-d dir |
-c cachefile] [
-D]
Lists pools available to import. If the
-d option is not specified, this command searches for devices in "/dev/dsk". The
-d option can be specified multiple times, and all directories are searched. If the device appears to be part of an exported pool, this command displays a summary of the pool with the name of the pool, a numeric identifier, as well as the
vdev layout and current health of the device for each device or file. Destroyed pools, pools that were previously destroyed with the "
zpool destroy" command, are not listed unless the
-D option is specified.
The numeric identifier is unique, and can be used instead of the pool name when multiple exported pools of the same name are available.
-c cachefile
Reads configuration from the given cachefile that was created with the " cachefile" pool property. This cachefile is used instead of searching for devices.
-d dir
Searches for devices or files in dir. The -d option can be specified multiple times.
-D
Lists destroyed pools only.
zpool import [
-o mntopts] [
-o property=
value] ... [
-d dir |
-c cachefile] [
-D] [
-f] [
-m] [
-R root] [
-F [
-n]]
-a
Imports all pools found in the search directories. Identical to the previous command, except that all pools with a sufficient number of devices available are imported. Destroyed pools, pools that were previously destroyed with the "
zpool destroy" command, will not be imported unless the
-D option is specified.
-o mntopts
Comma-separated list of mount options to use when mounting datasets within the pool. See zfs(1M) for a description of dataset properties and mount options.
-o property=value
Sets the specified property on the imported pool. See the "Properties" section for more information on the available pool properties.
-c cachefile
Reads configuration from the given cachefile that was created with the " cachefile" pool property. This cachefile is used instead of searching for devices.
-d dir
Searches for devices or files in dir. The -d option can be specified multiple times. This option is incompatible with the -c option.
-D
Imports destroyed pools only. The -f option is also required.
-f
Forces import, even if the pool appears to be potentially active.
-F
Recovery mode for a non-importable pool. Attempt to return the pool to an importable state by discarding the last few transactions. Not all damaged pools can be recovered by using this option. If successful, the data from the discarded transactions is irretrievably lost. This option is ignored if the pool is importable or already imported.
-a
Searches for and imports all pools found.
-m
Allows a pool to import when there is a missing log device. Recent transactions can be lost because the log device will be discarded.
-R root
Sets the "cachefile" property to "none" and the "altroot" property to " root".
-N
Import the pool without mounting any file systems.
-n
Used with the -F recovery option. Determines whether a non-importable pool can be made importable again, but does not actually perform the pool recovery. For more details about pool recovery mode, see the -F option, above.
zpool import [
-o mntopts] [
-o property=
value] ... [
-d dir |
-c cachefile] [
-D] [
-f] [
-m] [
-R root] [
-F [
-n]]
pool |
id [
newpool]
Imports a specific pool. A pool can be identified by its name or the numeric identifier. If
newpool is specified, the pool is imported using the name
newpool. Otherwise, it is imported with the same name as its exported name.
If a device is removed from a system without running "
zpool export" first, the device appears as potentially active. It cannot be determined if this was a failed export, or whether the device is really in use from another host. To import a pool in this state, the
-f option is required.
-o mntopts
Comma-separated list of mount options to use when mounting datasets within the pool. See zfs(1M) for a description of dataset properties and mount options.
-o property=value
Sets the specified property on the imported pool. See the "Properties" section for more information on the available pool properties.
-c cachefile
Reads configuration from the given cachefile that was created with the " cachefile" pool property. This cachefile is used instead of searching for devices.
-d dir
Searches for devices or files in dir. The -d option can be specified multiple times. This option is incompatible with the -c option.
-D
Imports destroyed pool. The -f option is also required.
-f
Forces import, even if the pool appears to be potentially active.
-F
Recovery mode for a non-importable pool. Attempt to return the pool to an importable state by discarding the last few transactions. Not all damaged pools can be recovered by using this option. If successful, the data from the discarded transactions is irretrievably lost. This option is ignored if the pool is importable or already imported.
-R root
Sets the "cachefile" property to "none" and the "altroot" property to " root".
-n
Used with the -F recovery option. Determines whether a non-importable pool can be made importable again, but does not actually perform the pool recovery. For more details about pool recovery mode, see the -F option, above.
-m
Allows a pool to import when there is a missing log device. Recent transactions can be lost because the log device will be discarded.
zpool iostat [
-T u |
d] [
-v] [
pool] ... [
interval[
count]]
Displays
I/O statistics for the given pools. When given an interval, the statistics are printed every
interval seconds until
Ctrl-C is pressed. If no
pools are specified, statistics for every pool in the system is shown. If
count is specified, the command exits after
count reports are printed.
-T u |
d
Display a time stamp.
Specify
u for a printed representation of the internal representation of time. See
time(2). Specify
d for standard date format. See
date(1).
-v
Verbose statistics. Reports usage statistics for individual vdevs within the pool, in addition to the pool-wide statistics.
zpool list [
-T u |
d] [
-Hv] [
-o props[,...]] [
pool] ... [
interval[
count]]
Lists the given pools along with a health status and space usage. If no
pools are specified, all pools in the system are listed. When given an
interval, the information is printed every
interval seconds until
Ctrl-C is pressed. If
count is specified, the command exits after
count reports are printed.
-T u |
d
Display a time stamp.
Specify
u for a printed representation of the internal representation of time. See
time(2). Specify
d for standard date format. See
date(1).
-H
Scripted mode. Do not display headers, and separate fields by a single tab instead of arbitrary space.
-p
Display numbers in parsable (exact) values.
-o props
Comma-separated list of properties to display. See the "Properties" section for a list of valid properties. The default list is "name, size, used, available, fragmentation, expandsize, capacity, dedupratio, health, altroot"
-v
Verbose statistics. Reports usage statistics for individual vdevs within the pool, in addition to the pool-wise statistics.
zpool offline [
-t]
pool device ...
Takes the specified physical device offline. While the
device is offline, no attempt is made to read or write to the device.
This command is not applicable to spares or cache devices.
-t
Temporary. Upon reboot, the specified physical device reverts to its previous state.
zpool online [
-e]
pool device...
Brings the specified physical device online.
This command is not applicable to spares or cache devices.
-e
Expand the device to use all available space. If the device is part of a mirror or raidz then all devices must be expanded before the new space will become available to the pool.
zpool reguid pool
Generates a new unique identifier for the pool. You must ensure that all devices in this pool are online and healthy before performing this action.
zpool reopen pool
Reopen all the vdevs associated with the pool.
zpool remove pool device ...
Removes the specified device from the pool. This command currently only supports removing hot spares, cache, and log devices. A mirrored log device can be removed by specifying the top-level mirror for the log. Non-log devices that are part of a mirrored configuration can be removed using the zpool detach command. Non-redundant and raidz devices cannot be removed from a pool.
zpool replace [
-f]
pool old_device [
new_device]
Replaces
old_device with
new_device. This is equivalent to attaching
new_device, waiting for it to resilver, and then detaching
old_device.
The size of
new_device must be greater than or equal to the minimum size of all the devices in a mirror or
raidz configuration.
new_device is required if the pool is not redundant. If
new_device is not specified, it defaults to
old_device. This form of replacement is useful after an existing disk has failed and has been physically replaced. In this case, the new disk may have the same
/dev/dsk path as the old device, even though it is actually a different disk.
ZFS recognizes this.
-f
Forces use of new_device, even if its appears to be in use. Not all devices can be overridden in this manner.
zpool scrub [
-s]
pool ...
Begins a scrub. The scrub examines all data in the specified pools to verify that it checksums correctly. For replicated (mirror or
raidz) devices,
ZFS automatically repairs any damage discovered during the scrub. The "
zpool status" command reports the progress of the scrub and summarizes the results of the scrub upon completion.
Scrubbing and resilvering are very similar operations. The difference is that resilvering only examines data that
ZFS knows to be out of date (for example, when attaching a new device to a mirror or replacing an existing device), whereas scrubbing examines all data to discover silent errors due to hardware faults or disk failure.
Because scrubbing and resilvering are
I/O-intensive operations,
ZFS only allows one at a time. If a scrub is already in progress, the "
zpool scrub" command terminates it and starts a new scrub. If a resilver is in progress,
ZFS does not allow a scrub to be started until the resilver completes.
-s
Stop scrubbing.
zpool set property=
value pool
Sets the given property on the specified pool. See the "Properties" section for more information on what properties can be set and acceptable values.
zpool split [
-n] [
-R altroot] [
-o mntopts] [
-o property=value]
pool newpool [
device ... ]
Splits off one disk from each mirrored top-level vdev in a pool and creates a new pool from the split-off disks. The original pool must be made up of one or more mirrors and must not be in the process of resilvering. The
split subcommand chooses the last device in each mirror vdev unless overridden by a device specification on the command line.
When using a
device argument,
split includes the specified device(s) in a new pool and, should any devices remain unspecified, assigns the last device in each mirror vdev to that pool, as it does normally. If you are uncertain about the outcome of a
split command, use the
-n ("dry-run") option to ensure your command will have the effect you intend.
-n
Displays the configuration that would be created without actually splitting the pool. The actual pool split could still fail due to insufficient privileges or device status.
-R altroot
Automatically import the newly created pool after splitting, using the specified altroot parameter for the new pool's alternate root. See the altroot description in the "Properties" section, above.
-o mntopts
Comma-separated list of mount options to use when mounting datasets within the pool. See zfs(1M) for a description of dataset properties and mount options. Valid only in conjunction with the -R option.
-o property=value
Sets the specified property on the new pool. See the "Properties" section, above, for more information on the available pool properties.
zpool status [
-xvD] [
-T u |
d ] [
pool] ... [
interval [
count]]
Displays the detailed health status for the given pools. If no
pool is specified, then the status of each pool in the system is displayed. For more information on pool and device health, see the "Device Failure and Recovery" section.
If a scrub or resilver is in progress, this command reports the percentage done and the estimated time to completion. Both of these are only approximate, because the amount of data in the pool and the other workloads on the system can change.
-x
Only display status for pools that are exhibiting errors or are otherwise unavailable. Warnings about pools not using the latest on-disk format will not be included.
-v
Displays verbose data error information, printing out a complete list of all data errors since the last complete pool scrub.
-D
Display a histogram of deduplication statistics, showing the allocated (physically present on disk) and referenced (logically referenced in the pool) block counts and sizes by reference count.
-T u |
d
Display a time stamp.
Specify
u for a printed representation of the internal representation of time. See
time(2). Specify
d for standard date format. See
date(1).
zpool upgrade
Displays pools which do not have all supported features enabled and pools formatted using a legacy ZFS version number. These pools can continue to be used, but some features may not be available. Use " zpool upgrade -a" to enable all features on all pools.
zpool upgrade -v
Displays legacy ZFS versions supported by the current software. See zpool-features(5) for a description of feature flags features supported by the current software.
zpool upgrade [
-V version]
-a |
pool ...
Enables all supported features on the given pool. Once this is done, the pool will no longer be accessible on systems that do not support feature flags. See
zpool-features(5) for details on compatibility with systems that support feature flags, but do not support all features enabled on the pool.
-a
Enables all supported features on all pools.
-V version
Upgrade to the specified legacy version. If the -V flag is specified, no features will be enabled on the pool. This option can only be used to increase the version number up to the last supported legacy version number.