I use XgimaNAS, an open source FreeBSD bases NAS appliance with 6x Western Digital 3TB (WD30EFRX) HDD's with a Areca ARC-1320-4i4x SAS HBA. Four of the drives are connected to a SansDigital 4-bay external enclosure, the other two are attached internally. Two drives are setup as a ZFS mirror and the remaining 4 in a RAIDZ2 configuration. It's been several years, and in that time I've had HDDs fail and replaced. The enclosure's power supply also failed at one point in history for which I had to replace the whole enclosure. The ZFS pools manage to survive all this turmoil very well.
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