Update:

I've spent some time trying to find out the behavior of vgextend and how to extend an existing LVM pool. After a while I've found this link, from the "libvirt-users" mailing list:

https://www.redhat.com/archives/libvirt-users/2013-September/msg00136.html

The interesting part is this:

" 
On 21/09/13 02:15, McEvoy, James wrote:

I looked around but could not find any info on how to expand a libvirt managed LVM storage pool.  I do not see any virsh command to do it
but I was successful using the vgexpand command to add some more storage once I destroyed the pools and then restarted it.
I'd like to verify that this is the proper way to grow the storage in a libvirt LVM storage pool.

It's not the proper way in principle, but since libvirt doesn't support to extend the volume groups for a logical pool yet, it's the only way now. One hint though, you can try to refresh the pool by command "virsh pool-refresh" after the volume 
group of the pool is extended. I.e, don't have to restart the pool."
In short, the recommended way to do it is using vgextend + pool-refresh. I've tried it and it works. But (there's always a "but") this process does not update the pool XML. And I'm not sure if it's supposed to.

I can submit a v1 patch with this implementation, but it would be awesome if a more experienced libvirt user/programmer could shed some light in this matter. I'm willing to send an email to libvirt-users ML if we do not have such expert here.

Thanks!

On 02/03/2014 10:00 AM, Aline Manera wrote:
On 01/31/2014 05:13 PM, Daniel H Barboza wrote:

On 01/31/2014 04:25 PM, Aline Manera wrote:

Hi Daniel,

Did you try to edit the pool xml and add a new device for it? Instead of doing it manually though vgextend command

For example:

virsh pool-destroy lvm-pool

virsh pool-edit lvm-pool
(add a new device for it)

virsh pool-start lvm-pool

I don't know if it is possible but we give it a try
Haven't tried it. Definitely worth a try.

Another question: maybe I could add some remove disk from LVM feature as well? If we support adding we should support removing... right? There is this caveat where removing a disk from a LVM can "corrupt" the data of the remaining pool. One solution to that would be to destroy/restart the LVM pool if a disk removal happens.

HHmmmm perhaps the removal of disks would be very similar to simply delete the pool and re-create it with fewer disks, so no point in trying to implement a new way to do the same thing .... thoughts?


Agree. We should not care about removal disks from a logical storage pool.
The best way to do it (from user view) is deleting the pool and creating a new one with few disks.


Regards,
Aline Manera

On 01/31/2014 11:42 AM, Daniel H Barboza wrote:
Hello!

I am almost delivering a first version of this feature but now I am having doubts in how it might work or not.

My implementation would use vgextend and add a disk to an existing LVM pool. The question is that, in this process, all existing data in the added partition will be deleted. Is this ok? We can warn the user about it, of course. But I am not sure if this is the intended design.

I've spoken with Aline a while ago and she agreed that the implementation would function similar to what we have today when creating a new LVM pool. We simply "do not care" about the potential data loss when adding the disk to an existing pool.

Any thoughts?


thanks!

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