I'm doing differential backups because I only need the baseline and the last differential to work. When I've had disk failures, this has not been immediately apparent. My rationale is that, with disk failues, the files most likely to be damaged are in the locations I access. With incremental backups, I figure I might be creating or picking up damaged files without knowing. With differential, I can go backwards through them until I find an undamaged file. So, for recovery I need the baseline + undamaged differential. Frequent baselines will pick up the damaged files before I know they are damaged, with no undamaged copy remaining. Until I run out of space, there would seem to be no good reason to take another baseline. The only good reason, I think, is to re-write the magnetic storage. The question becomes, how long do I trust my active backup disk to retain data? Surely, it's at least a year? Or two. A new full backup every week is wearing the mechanics, so that increases the chance of failure. I conclude that differentials, until I need to clear space is the way to go.
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