[gentoo-user] Re: Suggestions for backup scheme?

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2024-02-04, Wols Lists <antlists@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.