jmtd → log → backup

Backups are something I don't do well. I hope to write a more thorough article about them at some point. For now, here are some tips.

Like most home users, I don't have access to a tape drive or jukebox for backups. I'm therefore looking for a solution that backs up to a local block device. I haven't ruled out a solution that backs up to DVD-Rs, but I haven't found a suitable one.

I first tried rsnapshot, which uses hard link trees to represent increments. I found that this resulted in enormous filesystem metadata, sufficient to cause the machine I was running it on (an embedded ARM system) to slow to a crawl. I'd recommend to avoid anything using this technique.

I more recently have been using rdiff-backup. This has appeared to work quite well for a number of years. However, it does not gracefully handle the backup volume being full, spewing python backtraces. This is compounded with some confusing use of temporary directies and not honouring $TMPDIR. This has been known about for years (1, 2). I've just independently discovered these problems for the second time. Aside from that, because it does not de-duplicate files, it is sensitive to large files being moved around in the source being backed up. It also cannot do a dry-run estimate of the disk space required for the next increment. So: time to move on.

Back in 2010 I discovered bup, an intriguing backup tool that used a git-style backing store. It's interesting enough that I packaged it and use it in a few situations, but I wouldn't rely on it for my main backups, for two reasons: one, it's not tried-and-tested enough yet (but that is rapidly being resolved), two: you can't get rid of old increments, so your backup volume will always increase in size over time, and never throw away old data. So, for now: move on.

Next on my list to try is Lars Wirzenius' obnam.