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This is a simple example setup in a 12-drive enclosure. 9 disks, a global hot-spare disk and two cache drives.

Previously, I would have used straight ZFS mirrors for performance and expandability (raidz VDEVs can't be expanded), but at this scale, the 9-disk 3x3 raidz1 setup consistently outperformed a 10-disk RAID mirror setup in random and sequential I/O.

See: http://i.imgur.com/SeSlmH8.png

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A set of 5 stripes of mirrors has the same problem that the comment brought up - losing the _wrong_ two disks loses all of your data.

In this case, going to raidz2 across all 12 disks would give an extra disk worth of capacity/performance with the ability to lose any 2 disks without data loss and going to raidz3 should give the same capacity/performance with the ability to lose any 3 disks without data loss.

Hot spares and monitoring. RaidZ2 across that number of drives is a performance nightmare and against ZFS best practices.

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