Tape Rotation with Bacula

I love the topic of backups. I say that because it's IT's dirty secret. No one should keep data in one place only, yet it's very difficult to set up a backup solution. Different organizations have different needs, and so backup software has to provide a lot of options. But the need for options means when you just want to get basic backup running quickly, it's a challenge.

This post is part of a series about rolling your own backup solution. There are other ways to do it, but I wanted to do my own solution one more time...

I'm backing up a Windows XP desktop and a Windows XP laptop, a Dell SC440 which is the VMWare host, plus a number of Linux VMs that provide my basic infrastructure: DNS, DHCP, file server, Subversion server, test platforms for software development, and the backup server itself.

I chose tape in part because I can take the backup off-site. I'll take a tape off-site once a week. That means I might lose a week's worth of work if my house burns down, but I'm not ready to invest in the time and effort to swap tapes every day, either.

The Bacula documentation has a good section on backup strategies, but none of them include mine. I'll have to figure it out myself.

Bacula manages tapes in a tape pool. A pool is just a group of tapes. (Bacula calls tapes "volumes".) I want to let Bacula fill up one tape per week before it uses another, which is the default behaviour. At the end of the week, I want to eject the tape and use another. I'll let Bacula automatically recycle the tapes, meaning that after a week (in my case), Bacula will reuse a tape, overwriting the old backups on it.

Anyway, I started with a rotation to do a full backup Sunday night, incremental backups all week, and then eject the tape Saturday night after the last incremental. With three tapes I would always have last week's tape off site, except on Sunday.

I really only got started when I realized that that's a lot of tape wear given that the off-site happens once a week and that I have a fair bit of disk space on my main server. So my next idea is:

Take a full backup Monday night to disk, and incrementals up to Sunday night. Then, Monday morning write the whole disk volume to tape and take it off-site. That way I only run the tape once a week, and hopefully in a scenario that minimizes the chance of shoe-shining. I'll write the data to disk without compression, and let hardware compression compress the data to tape.

This also has the nice property that last week's backups are also on the disk (if I have enough disk space), so if I need a file I can get it from disk rather than retrieving the tape.