Re: Is anyone using btrfs send/receive for backups instead of rsync?

[Marc MERLIN <marc@merlins.org>]

On Mon, Dec 30, 2013 at 04:05:03PM +0000, Chris Mason wrote:
> On Sat, 2013-12-28 at 10:20 -0800, Marc MERLIN wrote:
> > On Sat, Dec 28, 2013 at 10:07:58AM -0800, Marc MERLIN wrote:
> > > For instance, if I use an existing rsync destination to start syncing
> > > btrfs snapshots to after that, and one file operation can't be applied
> > > because let's say the destination file it's supposed to be applied to,
> > > isn't there?
> > 
> > I should have written more: I'm guessing what happens is that the btrfs
> > receive fails/aborts, I get an error, I then run a manual rsync to reset
> > everything to a good known state, and then continue the btrfs
> > send/receive after that?
> 
> Btrfs send/receive works by matching state between snapshots on the
> sending and receiving end.  If you update the files manually on the
> receiving end (say with rsync), it can't merge the states anymore.

I got that, but it wasn't quite my question :)

I understand that btrfs receive cannot apply file changes if the
destination filesystem isn't in a file state that's identical to the source
one.

I'm just not too sure how the destination FS needs to be configured so
that btrfs receive can work with it.

1) Does it need to be an exact byte for byte copy of the block device the
source was on?

2) Or can the destination be seeded with a full rsync or cp -a and can btrfs receive
take over from there?

3) Then, if I hit a bug where something doesn't get synced right, and I run
rsync to fix or verify that the two FS are indeed identical file-wise
like they're supposed to, if rsync fixes something, are you saying that
it'll stop btrfs receive from working after that?

Thanks,
Marc
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