Creating a ZFS Storage Pool With Cache Devices

You can create a storage pool with cache devices to cache storage pool data. For example:

# zpool create tank mirror c2t0d0 c2t1d0 c2t3d0 cache c2t5d0 c2t8d0
# zpool status tank
  pool: tank
 state: ONLINE
 scrub: none requested
config:

        NAME        STATE     READ WRITE CKSUM
        tank        ONLINE       0     0     0
          mirror-0  ONLINE       0     0     0
            c2t0d0  ONLINE       0     0     0
            c2t1d0  ONLINE       0     0     0
            c2t3d0  ONLINE       0     0     0
        cache
          c2t5d0    ONLINE       0     0     0
          c2t8d0    ONLINE       0     0     0

errors: No known data errors

Consider the following points when determining whether to create a ZFS storage pool with cache devices:

• Using cache devices provides the greatest performance improvement for random-read workloads of mostly static content.
• Capacity and reads can be monitored by using the zpool iostat command.
• Single or multiple cache devices can be added when the pool is created. They can also be added and removed after the pool is created. For more information, see Example 4–4.
• Cache devices cannot be mirrored or be part of a RAID-Z 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 a RAID-Z configuration. The content of the cache devices is considered volatile, similar to other system caches.