[linux-lvm] lvm/openstack: stripe all volumes and distribute them round robin on PVs

[David Teigland]

On Wed, May 10, 2017 at 01:13:37PM +0200, Bernd wrote:
> Hello,
> 
> when using local lvm2 logical volumes for OpenStack Nova ephemeral pool
> then the created logical volumes are linear (not striped) and what is worse
> than that, all volumes are allocated on the same first physical volume
> (until it is filled up).
> 
> I made a ServerFault question about that:
> 
> https://serverfault.com/questions/849088/automatically-distribute-lvm-stripes-for-specific-lvm2-vg-on-linux/849255#849255
> 
> It was suggested that raid_stripe_all_devices should help (to turn on
> striping by default), but it did not. So I went ahead and patched the
> lvm.py of nova to turn the striping on. However I still wonder if there is
> a lvm option (allocation policy for that).
> 
> Besides that, it looks like it is still creating the first stripe on the
> first device. It would make more sense to have it (even in the linear case)
> to round robin the LVs. Because first of all it might be the most busy part
> of the volume and secondly it helps for keeping room for expanding volumes.
> 
> Is there anything planned in this direction?

If you're concerned with placement of LVs on PVs, I'd probably skip
striping and add some logic specifying different PVs directly:

lvcreate -n name -L size VG PV ...

means the LV will be created using only the specified PVs.