[ovirt-devel] vdsm disabling logical volumes

[Jiri Moskovcak]

On 05/04/2014 07:57 PM, Nir Soffer wrote:
> ----- Original Message -----
>> From: "Jiri Moskovcak" <jmoskovc at redhat.com>
>> To: devel at ovirt.org
>> Sent: Sunday, May 4, 2014 8:08:33 PM
>> Subject: [ovirt-devel] vdsm disabling logical volumes
>>
>> Greetings vdsm developers!
>>
>> While working on adding ISCSI support to the hosted engine tools, I ran
>> into a problem with vdms. It seems that when stopped vdsm deactivates
>> ALL logical volumes in it's volume group and when it starts it
>> reactivates only specific logical volumes. This is a problem for hosted
>> engine tools as they create logical volumes in the same volume group and
>> when vdsm deactivates the LVs the hosted engine tools don't have a way
>> to reactivate it, because the services drop the root permissions and are
>> running as vdsm and apparently only root can activate LVs.
>
> Can you describe what volumes are you creating, and why?

We create hosted-engine.lockspace (for sanlock) and 
hosted-engine.metadata (keeps data about hosted engine hosts)

>
>> So far the
>> only suitable solution seems to be to change vdsm to only
>> deactivate/activate it's own LVs.
>
> This sounds reasonable. You can add a list of hosted engine lv names
> and skip these volumes when deactivating vdsm volumes.

- this sounds a bit suboptimal, vdsm already has list of it's LVs, so it 
can just disable only LVs known to it, otherwise we would have to change 
the list everytime we add some LV to the group

>
> Another solution is to tag hosted engine lvs, and have vdsm ignore
> lvs that contains this tag.

- this sounds good, because if we teach vdsm to ignore LVs with some tag 
we can add new LVs in future without changing vdsm. This however applies 
also to the solution where vdsm only disables it's own LVs, so it 
depends on vdsm devels which solution they find better. I think the 
solution without tags is better, because is simpler and others (like 
hosted-engine) can just createlv and don't bother with tags..

--Jirka

>
> Nir
>