Tuesday, June 21, 2005

Unison keeps directories in sync

I started using Unison today. It was the missing part of my backup strategy. My backup strategy is to have mondorescue run on each of my linux servers once a day. This creates one or more .iso files that can be burned directly to a cd, which would be bootable. Therefore, even if the system is not bootable, you can still restore with this cd. You can also use mondo directly and restore from the .iso file.

Once the .iso is created locally on the server, I use rsync to transfer it to a repository, where I store all my backups on a removable IDE drive. I have 2 drives like that, and I wanted to be able to bring one home every weekend, to make sure we don't loose data in case of a fire. I didn't need Unison just for that. The thing is that this server is also a repository for Symantec Ghost images, and I wanted to always have the most recent images on the hard drive. The solution? Well, I tried a simple tar, but that lasts 30 minutes. Unison recognizes which files has changed and copies only those ones. So if no image has changed, it takes about 1 second do complete.


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