Re: cloning single-device btrfs file system onto multi-device one

[Stephane Chazelas <stephane.chazelas@gmail.com>]

2011-03-23 12:13:45 +0700, Fajar A. Nugraha:
> On Mon, Mar 21, 2011 at 11:24 PM, Stephane Chazelas
> <stephane.chazelas@gmail.com> wrote:
> > AFAICT, compression is enabled at mount time and would
> > only apply to newly created files. Is there a way to compress
> > files already in a btrfs filesystem?
> 
> You need to select the files manually (not possible to select a
> directory), but yes, it's possible using "btrfs filesystem defragment
> -c"
[...]

Thanks. However I find that for files that have snapshots, it
ends up increasing disk usage instead of reducing it (size of
the file + size of the compressed file, instead of size of the
file).

If I do the btrfs fi de on both the volume and its snapshot, I
end up with some benefit only if the compression ratio is over
2 (and with more snapshots, there's little chance of getting any
benefit at all). Also, with dozens of snapshots on a 4TB volume,
it's likely to take weeks to do.

Is there a way around that?

Thanks
Stephane