[Qemu-devel] Re: BTRFS: Unbelievably slow with kvm/qemu

[Giangiacomo Mariotti <gg.mariotti@gmail.com>]

On Mon, Jul 12, 2010 at 9:09 AM, Michael Tokarev <mjt@tls.msk.ru> wrote:
>
> This looks quite similar to a problem with ext4 and O_SYNC which I
> reported earlier but no one cared to answer (or read?) - there:
> http://permalink.gmane.org/gmane.linux.file-systems/42758
> (sent to qemu-devel and linux-fsdevel lists - Cc'd too).  You can
> try a few other options, esp. cache=none and re-writing some guest
> files to verify.
>
> /mjt
>
Either way, changing to cache=none I suspect wouldn't tell me much,
because if it's as slow as before, it's still unusable and if instead
it's even slower, well it'd be even more unusable, so I wouldn't be
able to tell the difference. What I can say for certain is that with
the exact same virtual hd file, same options, same system, but on an
ext3 fs there's no problem at all, on a Btrfs is not just slower, it
takes ages.

-- 
Giangiacomo