Migrating ZFS Storage Pools
Occasionally, you might need to move a storage pool between machines. To do so, the storage devices must be disconnected from the original machine and reconnected to the destination machine. This task can be accomplished by physically recabling the devices, or by using multiported devices such as the devices on a SAN. ZFS enables you to export the pool from one machine and import it on the destination machine, even if the machines are of different endianness. For information about replicating or migrating file systems between different storage pools, which might reside on different machines, see Saving and Restoring ZFS Data.
Preparing for ZFS Storage Pool Migration
Storage pools should be explicitly exported to indicate that they are ready to be migrated. This operation flushes any unwritten data to disk, writes data to the disk indicating that the export was done, and removes all knowledge of the pool from the system.
If you do not explicitly export the pool, but instead remove the disks manually, you can still import the resulting pool on another system. However, you might lose the last few seconds of data transactions, and the pool will appear faulted on the original machine because the devices are no longer present. By default, the destination machine refuses to import a pool that has not been explicitly exported. This condition is necessary to prevent accidentally importing an active pool that consists of network attached storage that is still in use on another system.
Exporting a ZFS Storage Pool
To export a pool, use the zpool export command. For example:
# zpool export tank
Once this command is executed, the pool tank is no longer visible on the system. The command attempts to unmount any mounted file systems within the pool before continuing. If any of the file systems fail to unmount, you can forcefully unmount them by using the -f option. For example:
# zpool export tank cannot unmount '/export/home/eschrock': Device busy # zpool export -f tank
If devices are unavailable at the time of export, the disks cannot be specified as cleanly exported. If one of these devices is later attached to a system without any of the working devices, it appears as “potentially active.” If ZFS volumes are in use in the pool, the pool cannot be exported, even with the -f option. To export a pool with an ZFS volume, first make sure that all consumers of the volume are no longer active.
For more information about ZFS volumes, see ZFS Volumes.
Determining Available Storage Pools to Import
Once the pool has been removed from the system (either through export or by forcefully removing the devices), attach the devices to the target system. Although ZFS can handle some situations in which only a portion of the devices is available, all devices within the pool must be moved between the systems. The devices do not necessarily have to be attached under the same device name. ZFS detects any moved or renamed devices, and adjusts the configuration appropriately. To discover available pools, run the zpool import command with no options. For example:
# zpool import pool: tank id: 3778921145927357706 state: ONLINE action: The pool can be imported using its name or numeric identifier. config: tank ONLINE mirror ONLINE c1t0d0 ONLINE c1t1d0 ONLINE
In this example, the pool tank is available to be imported on the target system. Each pool is identified by a name as well as a unique numeric identifier. If multiple pools available to import have the same name, you can use the numeric identifier to distinguish between them.
Similar to the zpool status command, the zpool import command refers to a knowledge article available on the web with the most up-to-date information regarding repair procedures for a problem that is preventing a pool from being imported. In this case, the user can force the pool to be imported. However, importing a pool that is currently in use by another system over a storage network can result in data corruption and panics as both systems attempt to write to the same storage. If some devices in the pool are not available but enough redundancy is available to have a usable pool, the pool appears in the DEGRADED state. For example:
# zpool import pool: tank id: 3778921145927357706 state: DEGRADED status: One or more devices are missing from the system. action: The pool can be imported despite missing or damaged devices. The fault tolerance of the pool may be compromised if imported. see: http://www.sun.com/msg/ZFS-8000-2Q config: tank DEGRADED mirror DEGRADED c1t0d0 UNAVAIL cannot open c1t1d0 ONLINE
In this example, the first disk is damaged or missing, though you can still import the pool because the mirrored data is still accessible. If too many faulted or missing devices are present, the pool cannot be imported. For example:
# zpool import pool: dozer id: 12090808386336829175 state: FAULTED action: The pool cannot be imported. Attach the missing devices and try again. see: http://www.sun.com/msg/ZFS-8000-6X config: raidz FAULTED c1t0d0 ONLINE c1t1d0 FAULTED c1t2d0 ONLINE c1t3d0 FAULTED
In this example, two disks are missing from a RAID-Z virtual device, which means that sufficient redundant data is not available to reconstruct the pool. In some cases, not enough devices are present to determine the complete configuration. In this case, ZFS doesn't know what other devices were part of the pool, though ZFS does report as much information as possible about the situation. For example:
# zpool import pool: dozer id: 12090808386336829175 state: FAULTED status: One or more devices are missing from the system. action: The pool cannot be imported. Attach the missing devices and try again. see: http://www.sun.com/msg/ZFS-8000-6X config: dozer FAULTED missing device raidz ONLINE c1t0d0 ONLINE c1t1d0 ONLINE c1t2d0 ONLINE c1t3d0 ONLINE Additional devices are known to be part of this pool, though their exact configuration cannot be determined.
Finding ZFS Storage Pools From Alternate Directories
By default, the zpool import command only searches devices within the /dev/dsk directory. If devices exist in another directory, or you are using pools backed by files, you must use the -d option to search different directories. For example:
# zpool create dozer mirror /file/a /file/b # zpool export dozer # zpool import -d /file pool: dozer id: 10952414725867935582 state: ONLINE action: The pool can be imported using its name or numeric identifier. config: dozer ONLINE mirror ONLINE /file/a ONLINE /file/b ONLINE # zpool import -d /file dozer
Importing ZFS Storage Pools
Once a pool has been identified for import, you can import it by specifying the name of the pool or its numeric identifier as an argument to the zpool import command. For example:
# zpool import tank
If multiple available pools have the same name, you can specify which pool to import using the numeric identifier. For example:
# zpool import pool: dozer id: 2704475622193776801 state: ONLINE action: The pool can be imported using its name or numeric identifier. config: dozer ONLINE c1t9d0 ONLINE pool: dozer id: 6223921996155991199 state: ONLINE action: The pool can be imported using its name or numeric identifier. config: dozer ONLINE c1t8d0 ONLINE # zpool import dozer cannot import 'dozer': more than one matching pool import by numeric ID instead # zpool import 6223921996155991199
If the pool name conflicts with an existing pool name, you can import the pool under a different name. For example:
# zpool import dozer zeepool
This command imports the exported pool dozer using the new name zeepool. If the pool was not cleanly exported, ZFS requires the -f flag to prevent users from accidentally importing a pool that is still in use on another system. For example:
# zpool import dozer cannot import 'dozer': pool may be in use on another system use '-f' to import anyway # zpool import -f dozer
Pools can also be imported under an alternate root by using the -R option. For more information on alternate root pools, see Using ZFS Alternate Root Pools.
Recovering Destroyed ZFS Storage Pools
You can use the zpool import -D command to recover a storage pool that has been destroyed. For example:
# zpool destroy tank # zpool import -D pool: tank id: 3778921145927357706 state: ONLINE (DESTROYED) action: The pool can be imported using its name or numeric identifier. The pool was destroyed, but can be imported using the '-Df' flags. config: tank ONLINE mirror ONLINE c1t0d0 ONLINE c1t1d0 ONLINE
In the above zpool import output, you can identify this pool as the destroyed pool because of the following state information:
state: ONLINE (DESTROYED)
To recover the destroyed pool, issue the zpool import -D command again with the pool to be recovered and the -f option. For example:
# zpool import -Df tank # zpool status tank pool: tank state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM tank ONLINE 0 0 0 mirror ONLINE 0 0 0 c1t0d0 ONLINE 0 0 0 c1t1d0 ONLINE 0 0 0 errors: No known data errors
If one of the devices in the destroyed pool is faulted or unavailable, you might be able to recover the destroyed pool anyway. In this scenario, import the degraded pool and then attempt to fix the device failure. For example:
# zpool destroy dozer # zpool import -D pool: dozer id: state: DEGRADED (DESTROYED) status: One or more devices are missing from the system. action: The pool can be imported despite missing or damaged devices. The fault tolerance of the pool may be compromised if imported. The pool was destroyed, but can be imported using the '-Df' flags. see: http://www.sun.com/msg/ZFS-8000-2Q config: dozer DEGRADED raidz ONLINE c1t0d0 ONLINE c1t1d0 ONLINE c1t2d0 UNAVAIL cannot open c1t3d0 ONLINE # zpool import -Df dozer # zpool status -x pool: dozer state: DEGRADED status: One or more devices could not be opened. Sufficient replicas exist for the pool to continue functioning in a degraded state. action: Attach the missing device and online it using 'zpool online'. see: http://www.sun.com/msg/ZFS-8000-D3 scrub: resilver completed with 0 errors on Fri Mar 17 16:11:35 2006 config: NAME STATE READ WRITE CKSUM dozer DEGRADED 0 0 0 raidz ONLINE 0 0 0 c1t0d0 ONLINE 0 0 0 c1t1d0 ONLINE 0 0 0 c1t2d0 UNAVAIL 0 0 0 cannot open c1t3d0 ONLINE 0 0 0 errors: No known data errors # zpool online dozer c1t2d0 Bringing device c1t2d0 online # zpool status -x all pools are healthy
Upgrading ZFS Storage Pools
If you have ZFS storage pools from a previous Solaris release, such as the Solaris 10 6/06 release, you can upgrade your pools with the zpool upgrade command to take advantage of the pool features in the Solaris 10 11/06 release. In addition, the zpool status command has been modified to notify you when your pools are running older versions. For example:
# zpool status pool: test state: ONLINE status: The pool is formatted using an older on-disk format. The pool can still be used, but some features are unavailable. action: Upgrade the pool using 'zpool upgrade'. Once this is done, the pool will no longer be accessible on older software versions. scrub: none requested config: NAME STATE READ WRITE CKSUM test ONLINE 0 0 0 c1t27d0 ONLINE 0 0 0 errors: No known data errors
You can use the following syntax to identify additional information about a particular version and supported releases.
# zpool upgrade -v This system is currently running ZFS version 3. The following versions are supported: VER DESCRIPTION --- -------------------------------------------------------- 1 Initial ZFS version 2 Ditto blocks (replicated metadata) 3 Hot spares and double parity RAID-Z For more information on a particular version, including supported releases, see: http://www.opensolaris.org/os/community/zfs/version/N Where 'N' is the version number.
Then, you can run the zpool upgrade command to upgrade your pools. For example:
# zpool upgrade -a
Note - If you upgrade your pools to the latest version, they will not be accessible on systems that run older ZFS versions.