Backup: Lost local reference

Backup: Lost local reference

[G EO]

I know I have discussed it already on this list, but unfortunately it
did no work out for me.
I am creating backups with btrfs send/receive, like described on the
wiki page https://btrfs.wiki.kernel.org/index.php/Incremental_Backup.

That means I have a subvolume "home", create a snapshot
"home-snapshot" and send it to the backup drive. Then the following
times I create another snapshot "home-snapshot-1" and send the
difference to the backup drive using "btrfs send -p home-snapshot
home-snapshot-1 | btrfs receive /path". For that to work I always need
to keep the last local reference (like home-snapshot) in this example.

Now I am in the unfortunate situation that I deleted the local
reference accidentally out of my own stupidity and wonder if there is
a way to determine the difference between the last snapshot on the
backup drive and the state of my sub-volume now.

I tried the following: I sent the last snapshot (in this example
home-snapshot-1) on the backup drive to an empty btrfs filesystem.
Then I created a read/write snapshot of this one
(home-snapshot-1-snap) and copied my whole current subvolume to the
read/write snapshot in the hope btrfs would only writes changes, but
that was hopeless, when sending the "diff -p" between the imported
snapshot (home-snapshot-1) and the read write snapshot
(home-snapshot-1-snap) back to the backup drive, it did not send any
differences but the whole subvolume (home-snapshot-1-snap).

So is there any way I can let compute the differences in order to
restore the old situation and continue with my incremental backups?

For information: I do not have any older local snapshots :-(, all of
the snapshot were deleted because of a regex problem in a script I
ran.

Re: Backup: Lost local reference

[Hugo Mills]

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On Sat, Jan 17, 2015 at 01:03:20PM +0100, G EO wrote:
> I know I have discussed it already on this list, but unfortunately it
> did no work out for me.
> I am creating backups with btrfs send/receive, like described on the
> wiki page https://btrfs.wiki.kernel.org/index.php/Incremental_Backup.
> 
> That means I have a subvolume "home", create a snapshot
> "home-snapshot" and send it to the backup drive. Then the following
> times I create another snapshot "home-snapshot-1" and send the
> difference to the backup drive using "btrfs send -p home-snapshot
> home-snapshot-1 | btrfs receive /path". For that to work I always need
> to keep the last local reference (like home-snapshot) in this example.
> 
> Now I am in the unfortunate situation that I deleted the local
> reference accidentally out of my own stupidity and wonder if there is
> a way to determine the difference between the last snapshot on the
> backup drive and the state of my sub-volume now.

   I think the short answer is, no, there isn't any way of doing it.

   Hugo.

> I tried the following: I sent the last snapshot (in this example
> home-snapshot-1) on the backup drive to an empty btrfs filesystem.
> Then I created a read/write snapshot of this one
> (home-snapshot-1-snap) and copied my whole current subvolume to the
> read/write snapshot in the hope btrfs would only writes changes, but
> that was hopeless, when sending the "diff -p" between the imported
> snapshot (home-snapshot-1) and the read write snapshot
> (home-snapshot-1-snap) back to the backup drive, it did not send any
> differences but the whole subvolume (home-snapshot-1-snap).
> 
> So is there any way I can let compute the differences in order to
> restore the old situation and continue with my incremental backups?
> 
> For information: I do not have any older local snapshots :-(, all of
> the snapshot were deleted because of a regex problem in a script I
> ran.

-- 
Hugo Mills             | Debugging is like hitting yourself in the head with
hugo@... carfax.org.uk | hammer: it feels so good when you find the bug, and
http://carfax.org.uk/  | you're allowed to stop debugging.
PGP: 65E74AC0          |                                        PotatoEngineer

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