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Solaris ZFS Administration Guide
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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: https://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: https://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: https://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

If devices exist in multiple directories, you can specify multiple -d options.

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: https://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: https://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:

https://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.


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