Dan's stuff right now keeps incremental backups (it uses rsync with the option to hardlink a new tree based on an old tree) and so the questions are e.g. when do you throw out the old backups, etc.
Maybe the right answer is to make the rsync-to-server thingy dead stupid (no incremental backup or anything like that, though maybe it should ensure each sync is atomic by having two copies) and rely on backing up the server for getting incrementals and so forth.
Use rdiff-backup (mentioned in other comments).
Set up some simple policy on how long to keep which backups.
Provide a simple 'restore lost file from backup' GUI (and commandline) utilities.
The "simple" policy I would advocate would be to keep incremental backups on this schedule:
One per day for the last week.
One per week for the last month[1]
One per month for the last N months, where N <= 14 [2], and have N automatically fluctuate as disk space on the server is consumed and freed. (May warn the user when it is about to be decreased.)
[1] Define "month" to mean "4 weeks" for simplicity.
[2] For a year, N = 52/4 = 13, and add one so you can get last April's tax return you inadvertantly deleted.
Regarding rdiff-backup: it keeps the incremental backups as "reverse" deltas from the latest, which works well for aging off the old backups and for disk usage.
Backing up data is one of those things that users don't tend to do. And when done, aren't done regularly, kept up to date, etc. Making it automatic, default behavior, and straightforward to restore from would do wonders to improve the state of most users. (Including me!) And, as a bonus, would be a great selling point for folks with a small or home office.
Thoughts?
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