On 07/04/2014 04:38 PM, Bob Williams wrote:
> I have a disc formatted as btrfs, on which is mounted /home.
>
> /home/bob is a regular directory.
>
> /home/bob/Documents is a btrfs subvolume
>
> /home is btrfs root
>
> If I do
>
> # mv /home/bob /home/bob_original
> # btrfs subvolume create /home/bob
> # mv /home/bob_original/* /home/bob/
> # rm /home/bob_original
>
> will the original subvolume /home/bob/Documents survive this
> operation, and will it now exist as a subvolume under the new
> subvolume /home/bob?
Yes.
A subvolume is a way to partition a btrfs file-system. You can think a
subvolume like a filesystem.
For objects like files and directory a move command between *different*
subvolumes is equal to a copy+remove. If fact is like you are moving data
between different file-systems.
Instead moving a subvolume in *its btrfs filesystem* is a cheap operation (is
like moving a link); this is true even if you move a subvolume between
different subvolumes.
To increase the speed when you move files between subvolumes (of the *same*
btrfs filesystem), you could do a "cp --reflink" + "rm" instead of a "mv"; eg
# mv subvolume-A/* subvolume-B/
is equal to
# cp -rf subvolume-A/* subvolume-B/
# rm -rf subvolume-A/*
but
# cp --reflink -R subvolume-A/* subvolume-B/
# rm -rf subvolume-A/
is faster because "cp --reflink" shared the data between source and
destination. This means that you are doing a copy (and a delete) of metadata
only.
>
> I realise it's best to create subvolumes progressively from the top of
> the filesystem tree, but this system originated as an ext4fs which was
> migrated to btrfs, and some sensible things got missed in all the
> excitement. ;-)
>
> Bob
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
--
gpg @keyserver.linux.it: Goffredo Baroncelli (kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
