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Date: Sun, 26 Jan 2014 02:49:22 +1000
From: Ken Drummond <btrfs@kendrummond.com>
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To: Marc MERLIN <marc@merlins.org>, Maxdamantus <maxdamantus@gmail.com>
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Subject: Re: Fwd: Is there a lightweight copy from one subvolume to another?
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On 25/01/2014 7:17 PM, Marc MERLIN wrote:
> On Sat, Jan 25, 2014 at 09:50:48PM +1300, Maxdamantus wrote:
>> Due to what I understand is some VFS limitation, you can only
>> reflink-copy between subvolumes under one Linux mountpoint. If
>> /mnt/btrfs1 provides access to all subvolumes, you should be able to
>> copy between them through that path, but you won't be able to copy
>> them across mounts, even `--bind` ones.
>
> That was exactly my understanding too.
>
>>> gargamel [mc]# cp -av --reflink=always misc/olympic Video/misc/
>>> `misc/olympic' -> `Video/misc/olympic'
>>> `misc/olympic/file.avi' -> `Video/misc/olympic/file.avi'
>>> cp: failed to clone `Video/misc/olympic/file.avi' from `misc/olympic/file.avi': Invalid cross-device link
>
> The test above was done in /mnt/btrfs_pool1 and failed as shown here.
>
> Yet
> gargamel:/mnt/btrfs_pool1# btrfs subvolume list .
> ID 257 top level 5 path misc
> ID 258 top level 5 path Video
> ID 259 top level 5 path media
> ID 260 top level 5 path Sound
> ID 261 top level 5 path zoneminder
> ID 262 top level 5 path other
>
> Aah, but it looks like this was my problem:
> 'Preparing to replace coreutils 8.13-3.2 (using .../coreutils_8.21-1_i386.deb) ...
>
> now cp --reflink works as expected.
>
> Thanks,
> Marc
>


If I recall correctly you also need a kernel >= 3.7.  Which I assume you 
have if this is now working.

Ken.