Creating ZFS Alternate Root Pools

The most common reason for creating an alternate root pool is for use with removable media. In these circumstances, users typically want a single file system, and they want it to be mounted wherever they choose on the target system. When an alternate root pool is created by using the zpool create -R option, the mount point of the root file system is automatically set to /, which is the equivalent of the alternate root value.

In the following example, a pool called morpheus is created with /mnt as the alternate root path:

# zpool create -R /mnt morpheus c0t0d0
# zfs list morpheus
NAME                   USED  AVAIL  REFER  MOUNTPOINT
morpheus              32.5K  33.5G     8K  /mnt

Note the single file system, morpheus, whose mount point is the alternate root of the pool, /mnt. The mount point that is stored on disk is / and the full path to /mnt is interpreted only in this initial context of the pool creation. This file system can then be exported and imported under an arbitrary alternate root pool on a different system by using -R alternate root value syntax.

# zpool export morpheus
# zpool import morpheus
cannot mount '/': directory is not empty
# zpool export morpheus
# zpool import -R /mnt morpheus
# zfs list morpheus
NAME                   USED  AVAIL  REFER  MOUNTPOINT
morpheus              32.5K  33.5G     8K  /mnt