I find all those NAS devices to be slow, Black Armour, Drobo, etc. I find it much more cost effective to build my own NAS using low end AMD mobo that has Raid 5 and then I have 6 Seagate 2TB 5900 drives. The AMD Raid software has an alerting function that can email you when a drive has a problem. You can also schedule drive scrubs and syncs to keep the RAID set healthy. With a 1gb NIC on the mobo I can peg the NIC, something I could never do with any off the shelf NAS. And the cost was competitive to a NAS unit.
Klipsch RP-280F / RC-62ii / RS-35 / RS-25
Dual PSA V1800s