Maybe it's the peskiness inherent in older tape backup systems that makes us so willing to bury the technology alive. Backing up to a single tape drive, usually one for every machine, meant lots of manual intervention, tape swapping and hardware to maintain. Even the advent of autoloaders and full-blown tape automation, which let you back up all your servers from a central location, haven't made life as good as it should be. Restores are a major pain, especially for those good doobies who store backup tapes off-site like you're supposed to. Then along comes cheap, ATA-based storage. It's not only quicker, but it also facilitates restores and elongates the backup window while leaving production systems unaffected. Makes you feel like you've died and gone to heaven.
Hold the phone a second. How are you going to get all that precious backed-up data off-site? Unless the guy lugging your tapes to the storage facility is built like King Kong and you've got the coin to buy all that disk a second time, it's not going to happen. Proponents of the "disk everywhere" strategy have a pat answer, of course: "Set up your disk array off-site and add connectivity."
But the truth is, that kind of bandwidth is expensive, and data stores are only getting larger. Furthermore, the cost of ATA storage is beginning to rival that of an individual tape with similar capacity. That much is clear. What is less apparent are the associated costs of spinning a disk. As heat dissipation stresses your data-center cooling system and the UPS load increases, electricity expenditures will rise up like a zombie in Dawn of the Dead. These are facts that most disk-to-disk vendors don't want to talk about.
Other disk downfalls include long-term storage and backward compatibility. Disk technology changes more rapidly than tape. And because of the need for long-term storage, tape generally has a much longer cycle and planned backward compatibility. Another advantage of tape is the very nature of the medium, which is separated from the read/write drive mechanism. So if your tape drive breaks, you simply plug in another piece of hardware and you're back in business. With disk, the media and read/write drive mechanisms are one piece, which should be serviced only in a class-100 clean room.