I believe there is a plan for expansion by adding devices to a RAID-Z -
I was asking this same question a year ago. IIRC: raid-z expansion is in
the works.
For now, you can add volumes to the zpool. Initially this doesnt sound
appealing, but what you can do is this:
Let's say you have 5 1B drives in a raidz2 in a zpool called "mypool".
Get 5 more drives, make another raidz2, and add that to "mypool". then
you have grown the zpool as well as kept raidz2 protection. the two
raidz2 volumes will stripe between each other within the zpool.
- - or wait for the device expansion on raidz
