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. 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). A whole disk can be specified by omitting the slice or partition designation. For example, sda is equivalent to /dev/sda. 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 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 sda sdb mirror sdc sdd

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.

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.

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.

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:

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.

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:

• 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.
• 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.

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.

One or more component devices is in the faulted state, and insufficient replicas exist to continue functioning. The underlying conditions are as follows:

• The device could be opened, but the contents did not match expected values.
• The number of I/O errors exceeds acceptable levels and the device is faulted to prevent further use of the device.

OFFLINE

The device was explicitly taken offline by the zpool offline command.

ONLINE

The device is online and functioning.

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.

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.

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.

Hot Spares

ZFS allows devices to be associated with pools as "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 spare vdev with any number of devices. For example,

# zpool create pool mirror sda sdb spare sdc sdd

Spares can be shared across multiple pools, and can be added with the zpool add command and removed with the zpool remove command. Once a spare replacement is initiated, a new 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.

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.

An in-progress spare replacement can be canceled 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.

Spares cannot replace log devices.

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 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:

# zpool create pool sda sdb log sdc

Multiple log devices can also be specified, and they can be mirrored. See the EXAMPLES section for an example of mirroring multiple log devices.

Log devices can be added, replaced, attached, detached, and imported and exported as part of the larger pool. Mirrored log devices can be removed by specifying the top-level mirror for the log.

Cache Devices

Devices can be added to a storage pool as "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.

To create a pool with cache devices, specify a cache vdev with any number of devices. For example:

# zpool create pool sda sdb cache sdc sdd

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.

The content of the cache devices is considered volatile, as is the case with other system caches.

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 (e.g, using 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 one of ONLINE, DEGRADED, FAULTED, OFFLINE, REMOVED, 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(8) 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:

ashift=ashift

Pool sector size exponent, to the power of 2 (internally referred to as 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 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.

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. 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 vdev_id(8) man page for more details. Autoreplace and autoonline require the ZFS Event Daemon be configured and running. See the zed(8) man page for more details.

bootfs=(unset)|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. Not all Linux distribution boot processes use the bootfs property.

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 will be empty.

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 minimum 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(8) 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.

listsnapshots=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. This property can also be referred to by its shortened name, listsnaps.

multihost=on|off

Controls whether a pool activity check should be performed during zpool import. When a pool is determined to be active it cannot be imported, even with the -f option. This property is intended to be used in failover configurations where multiple hosts have access to a pool on shared storage. When this property is on, periodic writes to storage occur to show the pool is in use. See zfs_multihost_interval in the zfs-module-parameters(5) man page. In order to enable this property each host must set a unique hostid. See genhostid(1) zgenhostid(8) spl-module-parameters(5) for additional details. 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 are 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 [-fgLnP] [-o property=value] 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.

-g

Display 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.

-L

Display real paths for vdevs 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.

-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.

-P

Display real paths for vdevs instead of only the last component of the path. This can be used in conjunction with the -L flag.

-o property=value

Sets the given pool properties. See the Properties section for a list of valid properties that can be set. The only property supported at the moment is ashift.

zpool attach [-f] [-o property=value] pool device new_device

Attaches new_device to the existing 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.

-o property=value

Sets the given pool properties. See the Properties section for a list of valid properties that can be set. The only property supported at the moment is ashift.

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 [-dfn] [-m mountpoint] [-o property=value]... [-o feature@feature=value]... [-O file-system-property=value]... [-R root] [-t tname] 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 ("."), colon (":"), space ("-"), 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.

-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.

-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.

-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(8).

-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.

-o property=value

Sets the given pool properties. See the Properties section for a list of valid properties that can be set.

-o feature@feature=value

Sets the given pool feature. See the zpool-features(5) section for a list of valid features that can be set. Value can be either disabled or enabled.

-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(8) for a list of valid properties that can be set.

-R root

Equivalent to -o cachefile=none -o altroot=root

-t tname

Sets the in-core pool name to tname while the on-disk name will be the name specified as the pool name pool. This will set the default cachefile property to none. This is intended to handle name space collisions when creating pools for other systems, such as virtual machines or physical machines whose pools live on network block devices.

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. If device may be re-added to the pool later on then consider the zpool offline command instead.

zpool events [-cfHv] [pool...]

Lists all recent events generated by the ZFS kernel modules. These events are consumed by the zed(8) and used to automate administrative tasks such as replacing a failed device with a hot spare. For more information about the subclasses and event payloads that can be generated see the zfs-events(5) man page.

-c

Clear all previous events.

-f

Follow mode.

-H

Scripted mode. Do not display headers, and separate fields by a single tab instead of arbitrary space.

-v

Print the entire payload for each event.

zpool export [-a] [-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 partitions, so that ZFS can label the disks with portable EFI labels. Otherwise, disk drivers on platforms of different endianness will not recognize the disks.

-a

Exports all pools imported on the system.

-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[,field]...] all|property[,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.

-o field

A comma-separated list of columns to display. name,property,value,source is the default value.

-p

Display numbers in parsable (exact) values.

zpool history [-il] [pool]...

Displays the command history of the specified pool(s) 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] [-c cachefile|-d dir]

Lists pools available to import. If the -d option is not specified, this command searches for devices in /dev. 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 -a [-DfmN] [-F [-n] [-T] [-X]] [-c cachefile|-d dir] [-o mntopts] [-o property=value]... [-R root] [-s]

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.

-a

Searches for and imports all pools found.

-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.

-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.

-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.

-N

Import the pool without mounting any file systems.

-o mntopts

Comma-separated list of mount options to use when mounting datasets within the pool. See zfs(8) 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.

-R root

Sets the cachefile property to none and the altroot property to root.

-s

Scan using the default search path, the libblkid cache will not be consulted. A custom search path may be specified by setting the ZPOOL_IMPORT_PATH environment variable.

-X

Used with the -F recovery option. Determines whether extreme measures to find a valid txg should take place. This allows the pool to be rolled back to a txg which is no longer guaranteed to be consistent. Pools imported at an inconsistent txg may contain uncorrectable checksum errors. For more details about pool recovery mode, see the -F option, above. WARNING: This option can be extremely hazardous to the health of your pool and should only be used as a last resort.

-T

Specify the txg to use for rollback. Implies -FX. For more details about pool recovery mode, see the -X option, above. WARNING: This option can be extremely hazardous to the health of your pool and should only be used as a last resort.

zpool import [-Dfm] [-F [-n] [-t] [-T] [-X]] [-c cachefile|-d dir] [-o mntopts] [-o property=value]... [-R root] [-s] 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.

-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.

-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.

-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.

-o mntopts

Comma-separated list of mount options to use when mounting datasets within the pool. See zfs(8) 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.

-R root

Sets the cachefile property to none and the altroot property to root.

-s

Scan using the default search path, the libblkid cache will not be consulted. A custom search path may be specified by setting the ZPOOL_IMPORT_PATH environment variable.

-X

Used with the -F recovery option. Determines whether extreme measures to find a valid txg should take place. This allows the pool to be rolled back to a txg which is no longer guaranteed to be consistent. Pools imported at an inconsistent txg may contain uncorrectable checksum errors. For more details about pool recovery mode, see the -F option, above. WARNING: This option can be extremely hazardous to the health of your pool and should only be used as a last resort.

-T

Specify the txg to use for rollback. Implies -FX. For more details about pool recovery mode, see the -X option, above. WARNING: This option can be extremely hazardous to the health of your pool and should only be used as a last resort.

-t

Used with newpool. Specifies that newpool is temporary. Temporary pool names last until export. Ensures that the original pool name will be used in all label updates and therefore is retained upon export. Will also set -o cachefile=none when not explicitly specified.

zpool iostat [[[-c SCRIPT] [-lq]]|-rw] [-T u|d] [-ghHLpPvy] [[pool...]|[pool vdev...]|[vdev...]] [interval [count]]

Displays I/O statistics for the given pools/vdevs. You can pass in a list of pools, a pool and list of vdevs in that pool, or a list of any vdevs from any pool. If no items are specified, statistics for every pool in the system are shown. When given an interval, the statistics are printed every interval seconds until ^C is pressed. If count is specified, the command exits after count reports are printed. The first report printed is always the statistics since boot regardless of whether interval and count are passed. However, this behavior can be suppressed with the -y flag. Also note that the units of K, M, G ... that are printed in the report are in base 1024. To get the raw values, use the -p flag.

-c [SCRIPT1[,SCRIPT2]...]

Run a script (or scripts) on each vdev and include the output as a new column in the zpool iostat output. Users can run any script found in their ~/.zpool.d directory or from the system /etc/zfs/zpool.d directory. Script names containing the slash (/) character are not allowed. The default search path can be overridden by setting the ZPOOL_SCRIPTS_PATH environment variable. A privileged user can run -c if they have the ZPOOL_SCRIPTS_AS_ROOT environment variable set. If a script requires the use of a privileged command, like smartctl(8), then it's recommended you allow the user access to it in /etc/sudoers or add the user to the /etc/sudoers.d/zfs file.

If -c is passed without a script name, it prints a list of all scripts. -c also sets verbose mode (-v).

Script output should be in the form of "name=value". The column name is set to "name" and the value is set to "value". Multiple lines can be used to output multiple columns. The first line of output not in the "name=value" format is displayed without a column title, and no more output after that is displayed. This can be useful for printing error messages. Blank or NULL values are printed as a '-' to make output awk-able.

The following environment variables are set before running each script:

VDEV_PATH

Full path to the vdev

VDEV_UPATH

Underlying path to the vdev (/dev/sd*). For use with device mapper, multipath, or partitioned vdevs.

VDEV_ENC_SYSFS_PATH

The sysfs path to the enclosure for the vdev (if any).

-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).

-g

Display 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.

-H

Scripted mode. Do not display headers, and separate fields by a single tab instead of arbitrary space.

-L

Display real paths for vdevs 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.

-p

Display numbers in parsable (exact) values. Time values are in nanoseconds.

-P

Display full paths for vdevs instead of only the last component of the path. This can be used in conjunction with the -L flag.

-r

Print request size histograms for the leaf ZIOs. This includes histograms of individual ZIOs ( ind) and aggregate ZIOs ( agg ). These stats can be useful for seeing how well the ZFS IO aggregator is working. Do not confuse these request size stats with the block layer requests; it's possible ZIOs can be broken up before being sent to the block device.

-v

Verbose statistics Reports usage statistics for individual vdevs within the pool, in addition to the pool-wide statistics.

-y

Omit statistics since boot. Normally the first line of output reports the statistics since boot. This option suppresses that first line of output.

-w

Display latency histograms:

total_wait: Total IO time (queuing + disk IO time). disk_wait: Disk IO time (time reading/writing the disk). syncq_wait: Amount of time IO spent in synchronous priority queues. Does not include disk time. asyncq_wait: Amount of time IO spent in asynchronous priority queues. Does not include disk time. scrub: Amount of time IO spent in scrub queue. Does not include disk time.

-l

Include average latency statistics:

total_wait: Average total IO time (queuing + disk IO time). disk_wait: Average disk IO time (time reading/writing the disk). syncq_wait: Average amount of time IO spent in synchronous priority queues. Does not include disk time. asyncq_wait: Average amount of time IO spent in asynchronous priority queues. Does not include disk time. scrub: Average queuing time in scrub queue. Does not include disk time.

-q

Include active queue statistics. Each priority queue has both pending ( pend) and active ( activ) IOs. Pending IOs are waiting to be issued to the disk, and active IOs have been issued to disk and are waiting for completion. These stats are broken out by priority queue:

syncq_read/write: Current number of entries in synchronous priority queues. asyncq_read/write: Current number of entries in asynchronous priority queues. scrubq_read: Current number of entries in scrub queue.

All queue statistics are instantaneous measurements of the number of entries in the queues. If you specify an interval, the measurements will be sampled from the end of the interval.

zpool labelclear [-f] device

Removes ZFS label information from the specified device. The device must not be part of an active pool configuration.

-f

Treat exported or foreign devices as inactive.

zpool list [-HgLpPv] [-o property[,property]...] [-T u|d] [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 ^C is pressed. If count is specified, the command exits after count reports are printed.

-g

Display 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.

-H

Scripted mode. Do not display headers, and separate fields by a single tab instead of arbitrary space.

-o property

Comma-separated list of properties to display. See the Properties section for a list of valid properties. The default list is name, size, alloc, free, fragmentation, expandsize, capacity, dedupratio, health, altroot.

-L

Display real paths for vdevs 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.

-p

Display numbers in parsable (exact) values.

-P

Display full paths for vdevs instead of only the last component of the path. This can be used in conjunction with the -L -flag.

-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-wise statistics.

zpool offline [-f] [-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.

-f

Force fault. Instead of offlining the disk, put it into a faulted state. The fault will persist across imports unless the -t flag was specified.

-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] [-o property=value] pool 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 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.

-o property=value

Sets the given pool properties. See the Properties section for a list of valid properties that can be set. The only property supported at the moment is ashift.

zpool scrub [-s | -p] pool...

Begins a scrub or resumes a paused 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 paused, the zpool scrub resumes it. If a resilver is in progress, ZFS does not allow a scrub to be started until the resilver completes.

-s

Stop scrubbing.

-p

Pause scrubbing. Scrub progress is periodically synced to disk so if the system is restarted or pool is exported during a paused scrub, the scrub will resume from the place where it was last checkpointed to disk. To resume a paused scrub issue zpool scrub again.

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 [-gLnP] [-o property=value]... [-R root] pool newpool [device ...]

Splits devices off pool creating newpool. All vdevs in pool must be mirrors and the pool must not be in the process of resilvering. At the time of the split, newpool will be a replica of pool. By default, the last device in each mirror is split from pool to create newpool.

The optional device specification causes the specified device(s) to be included in the new pool and, should any devices remain unspecified, the last device in each mirror is used as would be by default.

-g

Display 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.

-L

Display real paths for vdevs 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.

-n

Do dry run, do not actually perform the split. Print out the expected configuration of newpool.

-P

Display full paths for vdevs instead of only the last component of the path. This can be used in conjunction with the -L -flag.

-o property=value

Sets the specified property for newpool. See the Properties section for more information on the available pool properties.

-R root

Set altroot for newpool to root and automatically import it.

zpool status [-c [SCRIPT1[,SCRIPT2]...]] [-gLPvxD] [-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.

-c [SCRIPT1[,SCRIPT2]...]

Run a script (or scripts) on each vdev and include the output as a new column in the zpool status output. See the -c option of zpool iostat for complete details.

-g

Display 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.

-L

Display real paths for vdevs 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.

-P

Display full paths for vdevs instead of only the last component of the path. This can be used in conjunction with the -L -flag.

-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).

-v

Displays verbose data error information, printing out a complete list of all data errors since the last complete pool scrub.

-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.

zpool sync [pool ...]

This command forces all in-core dirty data to be written to the primary pool storage and not the ZIL. It will also update administrative information including quota reporting. Without arguments, zpool sync will sync all pools on the system. Otherwise, it will sync only the specified pool(s).

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 zfs-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.