I think the DX-30 is dead sexy. Three TBs of storage in 2U? Acts like disk but looks like tape? What's not to like? It certainly wins on the coolness factor. However, there are advantages and disadvantages to each of the three "genres" of virtual tape products.
Pure JBOD/RAID arrays are the least expensive of the lot but you are relegated to using RAID 1+0 or 5 here, decreasing the capacity or speed. They are harder to share than either of the other two, as you would need a globally writable, SAN-based filesystem to share it.
Virtual tape libraries, such as the DX-30 or one of the above RAID arrays using a product like Alacritus' virtual tape library software, are also very interesting. They potentially offer better raw throughput than the other options as there is no filesystem in between the disks and the backup applications. You're writing straight to raw disk. However, if you decide to multiplex to these devices they will probably suffer the same difficulties as tape-based products when you attempt to restore one stream out of the larger stream. (This is because the backup products do not/cannot intelligently skip over the blocks they don't need in a multiplexed stream. What they do is read them all and discard what they don't want.)
ATA-based filers, like Network Appliance's NearStore, appear to be the most versatile of the three choices. They are easily shared by multiple backup servers via NFS or CIFS and they do not suffer the multiplexing issue discussed above. The reason is that when backup products write to a disk device they tend to send every stream to its own filename. Even if you multiplex, you still end up with a single stream per backup. This allows you to multiplex on the front end if you want and easily demultiplex when creating offsite copies.
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This was first published in May 2002