BTRFS vs LVM for VM storage

[Ric Wheeler]

On 03/02/2011 10:30 PM, Hugo Osvaldo Barrera wrote:
> On 02/03/11 11:23, Richard W.M. Jones 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)?
>>
>> Rich.
>>
> Support for LVM won't be dropped anyway, this kind of usage can go on,
> and you can just user a separate disk/partition for doing the same thing
> you are doing now (presumably, with qemu).

We have no intention to drop LVM or device mapper - btrfs as a project has 
always intended to reuse existing code where possible.

Clearly, some bits will always be different but over time we should see more 
commonality as we increase our re-use.

> I do the same thing on a second disk, and wouldn't mind re-installing
> fedora en my primary on some-other-fs.
>
> I DO worry about how safe the FS is.
>
> I used BTRFS in ubuntu 10.10 on my GFs laptop, and SUDDENLY one day she
> ran out of battery, and when she re-booted the whole partition was
> empty.  I have not trusted BTRFS since.
>

It is really critical for btrfs to have properly enabled write barriers if your 
disk has the write cache enabled.

A big focus currently is to get the btrfs recovery tool wrapped up to help 
recover from a bad shutdown or other corruptions & we will be ramping up testing 
for power failures, etc.

Ric