I’ve long feared the use of CD-R and DVD-R as backup media. They are fundamentally unstable technologies. The burn might look good, and it might verify, but 1 year later I might not be able to read the data. I know tape is a great deal more stable, but I’ve often been put off by the high cost of tape drives.
Now I’m about to put a new machine on-line. Along with two friends/colleagues, we’ve purchased a 1U rack mount server. It’s a dual PIII 1.4GHz machine, 2GB of RAM, and a mirrored pair of 250GB drives. We’ve replaced all the moving parts in the server (the drives are new), and are being quite fastidious in our design and setup of the system. Our goal is to make the administration as simple as possible while allowing for a diverse number of users and uses. I’m confident, based on our experiences with our Bytemark virtual machine, that we’ll have a great box in place.
What’s the missing link? Backups. We’ve got complete sensing on the machine, so if one of the drives in the RAID array tanks, we’ll know by email, SMS, and every other messaging mechanism known to us that something’s gone wrong. I’m developing a little language for specifying backups over the filesystem, databases (both Postrgres and MySQL databases run on the machine), Subversion, and anything else that comes up needing to be backed up. Those backups will go first to disk, and then off-site.
But where then? Even with a clean, automated framework for moving data off the server, that leaves me in a position where I need to store the backups in some kind of safe way. This post is just me exploring the cost and reliability benefits of several different options.
| Solution | Drive cost | £/GB Low | £/GB High | Shelf life | Notes | Total £/GB |
| DVD | £40 | 0.02 | 0.09 | 6m – 2y | £50 | |
| Tape (Camcorder) | £280 | 0.17 | 0.50 | 3y – 10y | 4, 5 | £300 |
| Tape Drive | £900 | 0.22 | 0.30 | 3y – 20y | 1, 2, 3 | £950 |
| Hard Drive (RAID1) | £200 | x | 1.20 | 2y – 4y | £200 |
Notes
- I’ve given tapes a 3y to 20yr life as good tape practice assumes re-tensioning every 2-3 years.
- Apple Store link for VXA2
- Exabyte page
- Carts for VXA2
- Coolatoola homepage for DV Backup
- Apple page for DV Backup
I’ve been through this before, but it was worth seeing again.
So, if I want my backups to last a long time, I need to put them on tape. I can do that most cheaply with software like DV Backup, which allows me to store data on miniDV tape, turning a consumer miniDV camcorder into a digital tape drive. This is almost certainly the most stable format I can affordably purchase.
A tape drive is simply out of the budget; there’s no way I can afford, at this time, a real tape drive. And while I could use a hard drive, the shelf life of a pair of drives isn’t actually that great. Tape will last much longer, although it presents issues of data migration. Still, I’d feel better/can more easily afford (at this time) having to re-tension a miniDV tape every 2-3 years than having to buy new drives every 2-3 years.
For the short term, I think I’ll be using DVD. Our backups are intended for restoration in case of catastrophic failure, and therefore we’re only interested in restoring the last weekly or monthly. As soon as I can afford it, I’ll purchase a miniDV camcorder and begin using that as a destination for monthly (full) backups, and will keep those for a relatively long period of time.