Suggested methods for full backup of XServe RAID data

Question

I know this is only peripherally related to the discussion topic, but since every other suggestion posted here is followed by the disclaimer that you should make a full backup of your data before proceeding with any major operations on your RAID arrays, I'd like to know what more experienced admins do in order to create a full backup for reasonably fast recovery in case of substantial data loss during maintenance/repair.
Our current "backup" availability is incremental optical disc archival (our data is mostly "write-once"), but this isn't entirely practical for recovery since it's over a terabyte of data. Since the connected server has a free hot-swappable SCSI drive bay as well as an interface for external SCSI devices, not to mention the fiber channel and ethernet interfaces, the options that I'd consider in order would be:
1. A handful of 150-500 Gb SCSI hard drives, rotated out of the hot-swappable bay
2. An external tape drive attached to the SCI interface (with appropriate tape size, maybe the LTO-2 with 200Gb native capacity?)
3. Some other external SCSI storage device
4. Larger optical disc archival (I hear there are technologies arriving in the near future)
5. Network-based option; remote seems impractical due to sheer size, but perhaps local?
The idea is to make a full backup (long-term solutions are superior of course) of 1-2 Tb of data on the XServe RAID before attempting major surgery. Suggestions for common, accepted, tested, efficient methods for accomplishing this would be greatly appreciated. I apologize if this thread isn't on-topic enough for some of you.
-Brian

Answer 1

Brian,
Tape IMO is kinda yucky (to steal a term from your average 3 year old). It's fairly slow to back up to, it's very slow to restore, and it's actually not that reliable by itself (I worked with a large enterprise customer who said their backups were successful about 70% of the time (!!!)).
That said, tape has the advantage that you can offsite it and archive it very cheaply, and the media are fairly cheap, so you can make lots of backups, so if one fails, you probably can restore the data from another tape.
Disks are more expensive initially, but end up being pretty reliable, and you get a lot more flexibility (plus, they're fast).
An emerging "best of both worlds" backup strategy is what's called disk to disk to tape, where you typically back up to another large "disk," for example a second Xserve RAID. Data is then backed up from the second disk to tape, which is taken offsite... thus tape is used for what it's best at (offsite archival). Restore can be from disk in most cases, which is 10-20x faster than restoring from tape. People use software packages like Netvault's Bakbone or Atempo's Time Navigator, which can handle the whole process, and it works quite well. The backup disks (e.g. the RAID) can be onsite, or can be at a backup site a couple KM away, attached via optical (this is preferable, for DR reasons).
For cases where a second Xserve RAID is prohibitively expensive, cheaper (and slower) RAID 5 enclosures like Wiebetech's RAIDtech can provide a large (say, 1.6 TB) RAID 5 volume, accessible over FW800 or SATA (not sure if they have a SATA-based one yet).