On 2024-02-04, Wols Lists <antli...@youngman.org.uk> wrote: > On 04/02/2024 06:24, Grant Edwards wrote: > >> I don't understand, are you saying that somehow your backup doesn't >> contain a copy of every file? >> > YES! Let's make it clear though, we're talking about EVERY VERSION of > every backed up file.
> And you need to get your head round the fact I'm not - actually - > backing up my filesystem. I'm actually snapshoting my disk volume, my > disk partition if you like. OK I see. That's a bit different than what I'm doing. I'm backing up a specific set of directory trees from a couple different filesystems. There are large portions of the "source" filesystems that I have no need to back up. And within those directory trees that do get backed up there are also some excluded subtrees. > Your strategy contains a copy of every file in your original backup, a > full copy of the file structure for every snapshot, and a full copy of > every version of every file that's been changed. Right. > My version contains a complete copy of the current backup and > (thanks to the magic of lvm) a block level diff of every snapshot, > which appears to the system as a complete backup, despite taking up > much less space than your typical incremental backup. If I were backing up entire filesystems, I can see how that would definitely be true. > To change analogies completely - think git. My lvm snapshot is like > a git commit. Git only stores the current HEAD, and retrieves > previous commits by applying diffs. If I "check out a backup" (ie > mount a backup volume), lvm applies a diff to the live filesystem. Got it, thanks.
