Craig Barratt wrote: > Les writes: > >> But will you still be able to restore the file state as of each separate >> run? Sometimes the reason you are restoring is that the current version >> is a mess. The issue could probably be avoided with a complete tree >> link copy before starting followed by in in-place update, but that is >> probably even less efficient. > > Yes, the exact state of each older backup can be re-created. > > As each backup occurs, two trees are operated on: > > - the in-place update of the newest complete backup > > - a new tree is created with the deltas to get to the > original, now older, backup. Eg: if a new file replaces > an old one, the old file is moved to this tree. > > This new tree becomes the second-most-recent backup, stored > as a set of deltas (changes) relative to the newest complete > backup. > > Each older backup in turn would be represented on disk as a set of > deltas from the more recent one. The only "filled" backup is the > newest one. To view or restore a particular backup, you start with > the most recent (complete) backup, and successively apply the deltas > to get to the older backup. > > It's just the time-reverse of what BackupPC does already: to view > or restore an incremental, it starts with the next older full and > applies the deltas (forward in time) for each incremental level. > > The new, proposed, layout would completely decouple the storage > from the backup type (ie: whether it was an incremental or full > the storage method would be the same). > > As I mentioned earlier, you most often view and restore the > most recent backup. So the penalty doing the delta merges > for old backups is minor. > > You can delete the oldest backup at any time, since nothing > depends on it. No longer will there be the issue of keeping > a full around because incrementals depend on it. There would > be no difference between expiry of incrementals and fulls - they > would be treated the same since they are stored the same way. > > As discussed earlier, the only tricky part is deleting a backup > that isn't the oldest (as needed for exponential expiry). That > requires you to merge two deltas into one. > > Craig >
Very interesting discussion. Here's a link to an article on backups that you've probably all seen, but it's very interesting: http://www.mikerubel.org/computers/rsync_snapshots/ -Rob ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ BackupPC-users mailing list BackupPC-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/backuppc-users http://backuppc.sourceforge.net/
