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Smarter grooming algorithms

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We use a disk-to-disk-to-tape strategy.


The grooming strategy "Retrospect's defined policy" doesn't really cut it. The disk backup sets over time get filled up with snapshots of old disks that are now scrapped, and they will never be kicked out of the backup set. To manually delete them takes a _lot_ of time, so that is no solution.


I see two possible solutions to this:


1. Enable the administrator to set an upper limit on how long a snapshot should be saved in the backup set. After that time, the snapshots will get kicked out. We would probably set that to 3 months or so.


2. Rethink the "save the last two snapshots of a disk, no matter what" strategy. An alternative would be that just the oldest snapshot always is groomed, no matter if it is one of the two last ones for a certain source. (Before the oldest snapshot is groomed, of course the snapshot sparsening algorithm should be tried, as is done now.) This should probably need to be combined with a minimum saving time, so that one can make sure that the snapshots manage to get to tape before they are groomed.


In additions, since grooming takes a _lot_ of time and can potentially happen on _each_ backup, if alternative 1 is not implemented, one would like the grooming algorithm to always take quite a chunk at a time, say it should always try to free up 10 percent or so. How much maybe should be user settable. When we tried to use disk backup sets with only grooming, many small backups took 8 hours or more just because it very often had to groom to make room for the files. This of course didn't work for us at all.





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