Replacing Devices in a Storage Pool

You can replace a device in a storage pool by using the zpool replace command.

If you are physically replacing a device with another device in the same location in a redundant pool, then you only need to identify the replaced device. ZFS recognizes that it is a different disk in the same location. For example, to replace a failed disk (c1t1d0) by removing the disk and replacing it in the same location, use the syntax similar to the following:

# zpool replace tank c1t1d0

If you are replacing a device in a storage pool with a disk in a different physical location, you will need to specify both devices. For example:

# zpool replace tank c1t1d0 c1t2d0

If you are replacing a disk in the ZFS root pool, see How to Replace a Disk in the ZFS Root Pool.

The basic steps for replacing a disk are:

• Offline the disk, if necessary, with the zpool offline command.

• Remove the disk to be replaced.

• Insert the replacement disk.

• Run the zpool replace command. For example:

  # zpool replace tank c1t1d0

• Put the disk back online with the zpool online command.

On some systems, such as the Sun Fire x4500, you must unconfigure a disk before you take it offline. If you are just replacing a disk in the same slot position on this system, then you can just run the zpool replace command as identified above.

For an example of replacing a disk on this system, see Example 11–1.

Keep the following considerations in mind when replacing devices in a ZFS storage pool:

• If you set the pool property autoreplace to on, then any new device, found in the same physical location as a device that previously belonged to the pool, is automatically formatted and replaced without using the zpool replace command. This feature might not be available on all hardware types.

• The replacement device must be greater than or equal to the minimum size of all the devices in a mirrored or RAID-Z configuration.

• When a replacement device that is greater in size than the device it is replacing is added to a pool, is not automatically expanded to its full size. The autoexpand pool property value determines whether a replacement LUN is expanded to its full size when the disk is added to the pool. By default, the autoexpand property is disabled. You can enable this property to expand LUN size before or after the larger LUN is added to the pool.

  In the following example, two 16-Gbyte disks in a mirrored pool are replaced with two 72-Gbyte disks. The autoexpand property is enabled after the disk replacements to expand the full LUN sizes.

  # zpool create pool mirror c1t16d0 c1t17d0 # zpool status pool: pool state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM pool ONLINE 0 0 0 mirror ONLINE 0 0 0 c1t16d0 ONLINE 0 0 0 c1t17d0 ONLINE 0 0 0 zpool list pool NAME SIZE USED AVAIL CAP HEALTH ALTROOT pool 16.8G 76.5K 16.7G 0% ONLINE - # zpool replace pool c1t16d0 c1t1d0 # zpool replace pool c1t17d0 c1t2d0 # zpool list pool NAME SIZE USED AVAIL CAP HEALTH ALTROOT pool 16.8G 88.5K 16.7G 0% ONLINE - # zpool set autoexpand=on pool # zpool list pool NAME SIZE USED AVAIL CAP HEALTH ALTROOT pool 68.2G 117K 68.2G 0% ONLINE -

• Replacing many disks in a large pool is time consuming due to resilvering the data onto the new disks. In addition, you might consider running the zpool scrub command between disk replacements to ensure that the replacement devices are operational and the data is written correctly.

• If a failed disk has been replaced automatically with a hot spare, then you might need to detach the spare after the failed disk is replaced. For information about detaching a hot spare, see Activating and Deactivating Hot Spares in Your Storage Pool.

For more information about replacing devices, see Resolving a Missing Device and Replacing or Repairing a Damaged Device.