Great thing about ZFS is that even with a single disk you get some benefits – data integrity being the most important. And all ZFS commands work perfectly well, for example status:
# zpool status pool: Data.Tertiary state: ONLINE config: NAME STATE READ WRITE CKSUM Data.Tertiary ONLINE 0 0 0 diskid/DISK-XXX.eli ONLINE 0 0 0
However, what if one disk is not sufficient any more? It is clear zpool add can be used to create striped pool for higher speeds. And it is clear we can add another device to make a three way mirror. But what if we want to convert solo disk to mirror configuration?
Well, in that case we can get creative with attach command giving it both disks as an argument:
# zpool attach Data.Tertiary diskid/DISK-XXX.eli diskid/DISK-YYY.eli
After a few seconds, our mirror is created with all our data intact:
# zpool status pool: Data.Tertiary state: ONLINE status: One or more devices is currently being resilvered. The pool will continue to function, possibly in a degraded state. action: Wait for the resilver to complete. config: NAME STATE READ WRITE CKSUM Data.Replica ONLINE 0 0 0 mirror-0 ONLINE 0 0 0 diskid/DISK-XXX.eli ONLINE 0 0 0 diskid/DISK-YYY.eli ONLINE 0 0 0 (resilvering)
PS: Yes, I use encrypted disks from
/dev/diskid/ as I used them in previous ZFS examples. If you want plain devices, just use
ada0 and companions instead.