I'm going to second NinjaStyle's comment about using disk space for backups.
Tapes are a terrible medium. The tape drives have a habit of destroying tapes when they kill themselves, the tapes themselves are fragile. Anyone ever have to have a DLT tape repaired from a broken leader?
You've got three choices -- Older tape drive technology, newer tape drive technology, and disks. Older tape drive technology would be LTO2. Guess what, it's only available in SCSI. Newer tape drives, such as LTO4, are much more expensive and mostly available in SAS. Disks, well, they're disks. Let's run the numbers:
CASE 1 -- obsolete tape technology:
- fast enough,
- reliable and proven technology
- 200gb uncompressed capacity
- 200gb uncompressed capacity
- You'll have to change tapes yourself
- Without two tape drives, duplicating backup images will be somewhat clumsy.
- You'll want a second tape drive anyhow in case one of them breaks.
- If your backups grow past one tape, you'll be in an world of hurt because you'll need to babysit the tape drive.
- You'll have a hard time restoring backups without the tape drive (see second concern).
CASE 2 -- Modern tape technology
- same as above, but 800gb uncompressed capacity
- because it is newer, it is less necessary to keep a spare around (ie it won't be discontinued between when you buy it and when you need the spare)
- the tapes are more expensive. Even though they're larger, sometimes you want two copies of your backups on 2 different media, and the cost of that just went up.
Case 3 -- JBOD
Now -- you wouldn't use this as a raid. You would mount each disk and format each disk individually, put individual filesystems on to these disks, and only keep the "active" disks inserted and mounted; the rest would not be plugged in or active in any way. You'll want to make each backup to 2 different disk drives, or at least automate duplicating the backup image from one disk to the other.
- More online storage
- faster random access
- easier to recover without any special gear (no need for a tape drive to recover from any backup)
- easier to expand -- any new sata disk is compatible with this, no need to stick to the same style of disks originally used.
- disks don't have the same shelf life as tapes
- disks are more fragile than tapes
- disks can be affected by the system more than tapes (think virus infection or rm -rf /)
- managing the backups is a bit more of a pain in the ass because you have to manage the image duplication your self or buy more expensive software.
In short -- the question of which interconnect to use is basically chosen for you by which sort of tape drive you use. Otherwise, how you do your backups is a matter of which engineering compromise you're willing to make. When I did backups, I preferred to do them straight to disk, but then I had several SATA <-> FC enclosures and several computers and would duplicate the images between the computers and the enclosures. You're probably not looking at quite the same level of infrastructure to support your backups. I've certainly seen LTO2 robots work very nicely.