BTRFS vs LVM for VM storage (was: Re: Plans for BTRFS in Fedora)

[Josef Bacik]

On Wed, Mar 2, 2011 at 9:23 AM, Richard W.M. Jones <rjones at redhat.com> wrote:
> On Tue, Feb 22, 2011 at 02:51:50PM -0500, Josef Bacik wrote:
>> 2) Fedora 16 ships without LVM as the volume manager and instead use
>> BTRFS's built in volume management, again just for the default.
>
> Sorry I'm a bit late on this gentle discussion, but I have one
> question about this:
>
> I use LVM to store virtual machines, one VM per LV, and it's very good
> for that.
>
> How is BTRFS's performance when used to store VMs (presumably they are
> stored as files)?
>

Good, but the problem is the default behavior of virt manager is to
use fsync for everything, you have to manually go in and set the
"Cache" to "None" so it will use O_DIRECT, and then it's just as fast
as anything else.  Not a big deal if you create everything via the
command line, kind of annoying if you do it via the GUI, tho all you
have to do is say "let me edit the options before starting this vm"
when you first create it, set the cache type and then do the install
and you are good to go.  Thanks,

Josef