Not only that, but if a hacker breaks in and all your backups are online, they can just as easily destroy them too. Or they can become corrupted due to a failure. Tapes are much more stable (unless you pass a magnet over them) and you can store them, as you said, offsite.
Snapshots are great for near-term recovery, and mirrors are even good for single-point disasters, but you always want tapes available in the event of a catastrophe.
Bruce
Re the benefits of tapes, I suppose it depends on your setting.
If network bandwidth is too expensive, tapes plus sneakernet makes a cheap, high-bandwidth network technology to get your backups off-site. If network bandwidth is available and cheaper than the manpower, I'll run rsync over ssh, thankee; manpower is the one part of computer systems and their support that refuses to get cheaper.
As for security, I regard that as an orthogonal question. Systems have to be secured, backups doubly so. If you don't have the backup system adequately secured, your backups can't be trusted. Even if they're spun onto tapes later. And _lots_ of people don't remove those tapes, witness the popularity of the really gigantic tape jukeboxes intended to make for no-human-intervention backup systems.
If your backup server is adequately secured, I'd generally rather just pile it up with enough disks, rather than messing with tapes.
-Bennett
Hmm, guess I don't agree that disks are cheaper than tape libraries. I've been working for some time on pricing out a 1-terabyte set of storage, and here's roughly what I've come up with:
1TB of disks, SCSI RAID array: 4.5 to 6 cents per MB 1TB of DVD-RAM jukebox + media: 2.6 to 3 cents per MB
The price for the DVD-RAM library solution above includes the software & drivers to control the library. These prices are from real quotes, maybe two months old at most.
Tape media (DLT7k) is way cheaper than DVD-RAM media, by the way. Take the following with a grain of salt, since I'm doing it on the fly here, but I'm seeing DVD-RAM media at the "old" 2.6GB density (single-sided), including a magazine, coming out at 1.2 cent per MB ($30 per disk).
DLT7k media is more like 0.1 cents per MB ($65 per cartridge, where we're seeing capacities running about 50 to 55GB per tape). Our ATL P1000 library with 2 drives was around $30k, if I remember right. Add that to a full complement of media (30 tapes), giving 1.6TB capacity, total cost comes to about $32 or $33k. Even if it's higher than that, it's still got a long way to go before it gets to the $40k we've been quoted seeing for 1 TB of RAID.
Plus I can take the tapes (or DVD-RAM disks) out of my library and buy more media, extending my off-line capacity even more cheaply.
Dunno, maybe the prices I'm seeing are out of whack, but tape just still seems cheaper.
Regards,
-
Bennett Todd -
Bruce Sterling Woodcock -
Marion Hakanson