Open Stack

On 06/13/2018 07:58 AM, Blair Bethwaite wrote:

> Is the collective wisdom to use LVM based instances for these use-cases? Putting
> a host filesystem with qcow2 based disk images on it can't help
> performance-wise... Though we have not used LVM based instance storage before,
> are there any significant gotchas? And furthermore, is it possible to use set IO
> QoS limits on these?

LVM has the drawback that deleting instances results in significant disk traffic 
while the volume is scrubbed with zeros.  If you don't care about security you 
can set a config option to turn this off.  Also, while this is happening I think 
your disk resource tracking will be wrong because nova assumes the space is 
available. (At least it used to be this way, I haven't checked that code recently.)

Also, migration and resize are not supported for LVM-backed instances.  I 
proposed a patch to support them (https://review.openstack.org/#/c/337334/) but 
hit issues and never got around to fixing them up.

Chris