I've just taken delivery of a spanking new 500GB LaCie Firewire drive for work. I've partitioned it in two, with the bulk of the space allocated for video data, but I've also made a backup partition for my laptop. I've wanted to try using rsync for ages, but I never really had a large enough hard drive spare to try it.
The great thing about
rsync is that you can do frequent incremental
backups (keeping snapshots of the state of your drive at various time
intervals), while not using much more space than a single backup,
and while allowing you to easily restore a whole directory structure
without having to piece together backup sets.
It manages this feat by using hard links, and rotating backup sets. In the latest set, only the files which have changed are backed up, but hard links are created for the rest of the files, so the latest backup appears to be (and to all intents and purposes is) a full copy of the source.
rsync is included in Tiger, but it can be a little tricky to set up a
script to back everything up, particularly if you want to back up
multiple but separate directories to a single destination. However,
rsnapshot provides a nice, easily
configured wrapper around
rsync. You can configure the number of
hourly, daily, weekly and monthly backups that get rotated, and you can
set multiple source paths to backup.
It works very nicely, but I've been trying to think of a good way to
automate starting it. Now that
cron is deprecated in Tiger, I'm
looking in to using
launchd to run the backups. The tricky part is
that I only want it to run if my Firewire drive is mounted, which is
only more or less in office hours.
rsnapshot does come with a little
script that checks whether the snapshot path is mounted before it runs
the process itself, but it would be nice to do it within
watchpaths property which is supposed to only start the
process if a path changes (which would happen if my drive was mounted).
The other snag is that I don't think that
launchd yet supports the
'*/4' style of time intervals (i.e. every 4 hours).
I'll try to construct something over the weekend, and test it on
Monday. If anyone has any tips for using
launchd as a cron
replacement, let me know!