Block level backups and grooming

[JamesOakley]

I've read the documentation on the new 9.x block-level backups feature. It looks great.

 

I was just wondering how it affects grooming. If Retrospect backs up a whole file each time, grooming just means removing unnecessary copies of a file, leaving enough to retain the desired snapshots. (Imagine a file that is backed up on 7 days in full: F, F1, F2, F3, F4, F5 and F6. To remove the snapshot on day 4, Retrospect simply removes the file F4)

 

Backing up incrementally, Retrospect cannot remove some backup instances of a file without making a restore impossible. (Imagine a file was backed up in full, F, and then over the next week there were 6 incremental backups, d1, d2, d3, d4, d5 and d6. To restore back to Day 5's snapshot, Retrospect would restore F, then apply the differentials d1, d2, d3, d4 and d5 in order. Suppose we now groom and wish to remove the snapshot on day 4. Retrospect cannot remove d4. If it did, so, it would become impossible to recover to day 5, because F+d1+d2+d3+d5 would not be correct).

 

So are some files now not groomed? Or does Retrospect merge in the diffs that it deletes, (so that d5 is replaced by a new one that contains d4+d5)? I'm curious to know how this would work - I don't want to start using the new feature, only to need to groom in 6 months time and then find that I've got a problem with what it's done, or to find that grooming doesn't free up much space because it can't really groom properly.

[Mayoff]

The new feature does not impact grooming.  Grooming will continue exactly has it has in the past.  Grooming is still based on the number of snapshots you have and those older snapshots get removed during a groom along with any parts of the file that are no longer needed to restore the data remaining within your backup set.   Retrospect will track which parts of a file are needed to restore from any available backup session.