You should have a tape drive for backup. Ideally, your tape backup should be able to image your entire disk. Choosing a tape drive used to be pretty complicated, with a plethora of different formats and media to chose from. It's much simpler now that the combination of cheap CD-ROM drives and huge hard disks has effectively killed off QIC and other sub-megabyte formats.
There are a bunch of non-tape niche technologies for backup, including floptical disks, Bernoulli boxes, Iomega and SyQuest removable drives, and magneto-optical drives. Ignore them all; they're half-assed attempts to combine a backup device with the fast random access needed for working storage that don't do either job very cost-effectively, especially when you consider the (high) cost of their media. Only magneto-optical drives are likely to have much of a future, and that only given improvements in access speed.
Digital Data Storage (DDS) capacities are a good match for today's multi-gigabyte drives (this is essentially the same technology as Digital Audio Tape or DAT). I'm told that Hewlett-Packard DDS devices are especially good, not surprising given HP's traditional obsession with reliability and overengineering stuff. All the DDSs I know about are SCSI devices.
At the high end, 8mm helical-scan tape (the stuff used in Sony camcorders) competes with DDS. This is a single-source tchnology, from Exabyte. Capacities are 2.2 and 5 gig, transfer speeds up around 500Kbytes/sec. However, a correspondent says ``Don't touch Exabyte. I've got three. All three have been sent back for warranty repair at least once.'' He also says ``A significant expense can be the cleaning tapes. Exabyte is notorious for this.'' So it's probably a good idea to stick with DDS if you have high-capacity requirements.
OTOH, Carl Renneberg <renneber@sci-log.apana.org.au> says of the Exabyte that his drive has proven to be rock steady and reliable, and recommends it with the following provisos:
You must, simply must, use the correct kind of tape. Do not use 8mm video cartridges - they leave junk on the drive's head, and have dropouts. They are simply not designed for storing data. Use only the data grade tape from Sony (or from Exabyte - Sony manufactures the tape, Exabyte relabels it).
Use the correct tape cleaner. Like tape cartridges, it's cheaper to buy the Sony brand than the Exabyte brand.
Carl has found that, where someone has had poor experience with Exabyte drives, it's because the owner - or the previous owner - did not take care of the drive, or used junk tapes.
Here's a quick summary of the major alternative DDS formats:
Table 2. DDS types
| Type | Megabytes (uncompressed) | Megabytes (compressed) | Speed (Kbytes/sec) |
|---|---|---|---|
| DDS-1 60-meter | 1300 | 2K-4K | 183-366 |
| DDS-1 90-meter | 2000 | 4K-8K | 183-366 |
| DDS-2 120-meter | 5000 | 7K-12K | 183-500 |
DDS tape drives (and tapes) come actually in four variants: DDS, DDS-DC, DDS-2, and DDS-3. These are supposed to be downward compatible (e.g. DDS-2 reads/writes DDS-DC but not vice versa.) DDS and DDS-DC use 60m and 90m tapes; the -DC version adds hardware compression. DDS (non-DC) should be considered obsolete. DDS-2 adds 120m tapes and denser recording:
There is also a yet-newer DDS-3 standard, with yet again higher density on the tape. DDS-3 is bleeding edge (high premium), but DDS-2 is coming down now, and can make the difference between single-tape and and multi-tape backups (which can often make the difference between daily backups and "why didn't I..." hand-wringing.)