I just wanted to contribute a good word about the Andre Lue's Eon storage server based on the formerly OpenSolaris now OpenIndiana release. I realize that many people are quite fond of FreeBSD and Linux based NAS appliances - but this Solaris implementation is particularly distinctive due to ZFS ; which thus far has saved the day with two disk failures over two years!
Eon is a stripped down Solaris that can be burned to a USB stick or Flash drive. It's quite small. This mode of installation allows you to completely avoid having the OS on your storage drives. This has the benefit of allowing you to quickly migrate your storage drives to a new server box in a dire failure such as a dead motherboard or server.
What makes ZFS special is it's management of the the storage pool. It uses strong block checksumming to detect and correct errors on disk. It does both striping and mirroring and the management of drive sets and controller groups is the most intuitive, painless and automated I've seen since touching an EMC storage box.
Protocol wise, I run CIFS, NFSv3 and iSCSI from the box. All of these sharing protocols are supported out of the box. Fileset sharing control does not require editing config files (i.e. no editing /etc/sharetab with vi!) All ZFS operations - from scrubbing, to mounting new FS, to sharing over network protocols is done with a single command line verb (zfs share).
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