Open Stack

On 06/23/2018 08:38 AM, Volodymyr Litovka wrote:
> Dear friends,
>
> I did some tests with making volume available without stopping VM. I'm using
> CEPH and these steps produce the following results:
>
> 1) openstack volume set --state available [UUID]
> - nothing changed inside both VM (volume is still connected) and CEPH
> 2) openstack volume set --size [new size] --state in-use [UUID]
> - nothing changed inside VM (volume is still connected and has an old size)
> - size of CEPH volume changed to the new value
> 3) during these operations I was copying a lot of data from external source and
> all md5 sums are the same on both VM and source
> 4) changes on VM happens upon any kind of power-cycle (e.g. reboot (either soft
> or hard): openstack server reboot [--hard] [VM uuid] )
> - note: NOT after 'reboot' from inside VM
>
> It seems, that all these manipilations with cinder just update internal
> parameters of cinder/CEPH subsystems, without immediate effect for VMs. Is it
> safe to use this mechanism in this particular environent (e.g. CEPH as backend)?

There are a different set of instructions[1] which imply that the change should 
be done via the hypervisor, and that the guest will then see the changes 
immediately.

Also, If you resize the backend in a way that bypasses nova, I think it will 
result in the placement data being wrong.  (At least temporarily.)

Chris


[1] 
https://wiki.skytech.dk/index.php/Ceph_-_howto,_rbd,_lvm,_cluster#Online_resizing_of_KVM_images_.28rbd.29