BTRFS send/receive limitations

BTRFS send/receive limitations

[Lists]

I read recently that you can't send/receive concurrent streams on the 
same filesystem, which begs the question of what is meant by a 
"filesystem". Is that to say that you can't send/receive snapshots on 
different subvolumes to the same "root filesystem"? Or that you can't 
send/receive multiple snapshots on the same subvolume? Can you 
send/receive a snapshot or subvolume to the same root filesystem?

-Ben

Re: BTRFS send/receive limitations

[Hugo Mills]

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On Fri, Apr 04, 2014 at 09:50:05AM -0700, Lists wrote:
> I read recently that you can't send/receive concurrent streams on the same
> filesystem, which begs the question of what is meant by a "filesystem". Is
> that to say that you can't send/receive snapshots on different subvolumes to
> the same "root filesystem"? Or that you can't send/receive multiple
> snapshots on the same subvolume? Can you send/receive a snapshot or
> subvolume to the same root filesystem?

   The restriction was on the same *filesystem* as a whole: there was
a global lock on the whole FS, which could cause deadlocks with send
and receive both accessing the same FS (any subvolumes). I don't
recall hearing about problems with two sends from different subvols on
the same FS, but that might just be because I wasn't paying attention.
:)

   I think those restrictions are gone now, in some patch in the
pipeline. Possibly for 3.15 -- I'm not sure if the patches made it
into 3.14.

   Hugo.

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