3:20 PM -- When Quantum introduced the DX-30, and therefore created the open systems virtual tape library market, I climbed right on the bandwagon. A VTL enabled backup admins to say goodbye to tape problems like library mechanical failures; tape drive shoe-shining, which made slow backups even slower; and multiplexing, which replaced the shoe-shining problem with slow restores and tape management headaches without forcing them to change their backup software or procedures.
Now that we're more than five years into the backup-to-disk era, I'm starting to have doubts. VTLs have made backups, especially the single file or object restores that fill up too much of a backup admin's day, significantly less painful -- but because they emulate tape libraries they're limited to the things tape drives can do.
On the plus side, an 8-GB Fibre Channel-attached VTL provides a well defined set of semantics for sharing the library, if not any given virtual tape drive, between multiple backup media servers and a high-bandwidth, low-protocol overhead connection to those media servers. NAS interfaces involve higher protocol overhead and are more significantly limited to 1-Gbit/s Ethernet for most backup targets and media servers. But affordable 10-Gbit/s Ethernet is just about here, and a good NFS, or even CIFS 2, implementation should get close enough for government work to FC performance.
My biggest problem with emulating tape is that today's streaming tape drives, unlike the 9-track reel-to-reel drives of "Colossus: The Forbin Project" fame, can't do block overwrites or block erases. If you hire a new sales manager from the International Wicket Corporation and he illegally brought their customer list with him and stored it on one of your servers, eventually your corporate counsel may promise to delete all copies of that file -- or even worse, the child porn some hacker saved to a server he took over on your network. But your backup software will be unable to delete just the offending files; it must copy everything else off the offending virtual tape to another and then delete the offending tapes.
What do you think? Are VTLs just an interim step to having backup software treat disk like disk? Or are we just too stuck in the way we've always done things to make the change?