[Original] OP here. I wrote this five years ago and it stands up pretty well. HP Microservers are a great device but if I were to build a new one today I'd look into using one of the many cheap ARM boards (NB: ZFS allegedly needs 64-bit to be stable) with disks in a USB-attached enclosure. Performance with USB3 should be enough for any home NAS and the hardware should come out even cheaper. There may even be ARM-base…
I'd recommend against using raid-z(X) on a USB enclosure. The throughput to each disk just isn't there. Also, my experiences using ZFS(onlinux) without any raid (i.e. single disk with "copies=" > 1) is that it wasn't very resilient against any kind of I/O error - even if the cable was bumped or something. This has resulted in the loss of a whole zpool and restore from backup.
Yikes. Is it similarly fragile in the event of sudden power loss?