ZFS: Adding a new mirror to an existing ZFS pool

  Mirrored vdevs are great for performance and it is quite straight-forward to add a mirrored vdev to an existing pool (presumably one with one or more similar vdevs already):  
zpool add [poolname] mirror [device01] [device02] [device03]
  If it’s a two-way mirror you will only have two devices in the above. An example for ZFS on Ubuntu with a pool named seleucus and two SSDs could look like:  
zpool add seleucus mirror ata-SAMSUNG_SSD_830_Series_S0XYNEAC705640 ata-M4-CT128M4SSD2_000000001221090B7BF9
  As always, it’s good practice to use the device name found in /dev/disk/by-id/ rather than the sda, sdb, sdc etc. names as the latter can change – the former do not.

How do you tell which zpool version you are running?

This is a question that crops up fairly regularly, as different operating systems support different zpool versions. Fortunately, it’s quite easy to find out which versions you are running – simply run:   # zpool upgrade   If you want a more detailed readout, including the features of the pool version you have, try:   # zpool upgrade -v   Your output should look something like this:   # zpool upgrade -v This system is currently running ZFS pool version 28. The following versions are supported: VER  DESCRIPTION —  ——————————————————– 1   Initial ZFS version 2   Ditto blocks (replicated metadata) 3   Hot spares and double parity RAID-Z 4   zpool history 5   Compression using the gzip algorithm 6   bootfs pool property 7   Separate intent log devices 8   Delegated administration 9   refquota and refreservation properties 10  Cache devices 11  Improved scrub performance 12  Snapshot properties 13  snapused property 14  passthrough-x aclinherit 15  user/group space accounting 16  stmf property support 17  Triple-parity RAID-Z 18  Snapshot user holds 19  Log device removal 20  Compression using zle (zero-length encoding) 21  Deduplication 22  Received properties 23  Slim ZIL 24  System attributes 25  Improved scrub stats 26  Improved snapshot deletion performance 27  Improved snapshot creation performance 28  Multiple vdev replacements For more information on a particular version, including supported releases, see the ZFS Administration Guide.   Or for the more simple command: # zpool upgrade   This system is currently running ZFS pool version 28. All pools are formatted using this version.