[ovirt-users] thin_check run on VM disk by host on startup ?!

[Nir Soffer]

On Wed, Aug 31, 2016 at 11:07 AM, Rik Theys <Rik.Theys at esat.kuleuven.be> wrote:
> On 08/31/2016 09:43 AM, Rik Theys wrote:
>> On 08/30/2016 04:47 PM, Nir Soffer wrote:
>>> On Tue, Aug 30, 2016 at 3:51 PM, Rik Theys <Rik.Theys at esat.kuleuven.be> wrote:
>>>> While rebooting one of the hosts in an oVirt cluster, I noticed that
>>>> thin_check is run on the thin pool devices of one of the VM's on which
>>>> the disk is assigned to.
>>>>
>>>> That seems strange to me. I would expect the host to stay clear of any
>>>> VM disks.
>>>
>>> We expect the same thing, but unfortunately systemd and lvm try to
>>> auto activate stuff. This may be good idea for desktop system, but
>>> probably bad idea for a server and in particular a hypervisor.
>>>
>>> We don't have a solution yet, but you can try these:
>>>
>>> 1. disable lvmetad service
>>>
>>>     systemctl stop lvm2-lvmetad.service lvm2-lvmetad.socket
>>>     systemctl mask lvm2-lvmetad.service lvm2-lvmetad.socket
>>>
>>> Edit /etc/lvm/lvm.conf:
>>>
>>>     use_lvmetad = 0
>>>
>>> 2. disable lvm auto activation
>>>
>>> Edit /etc/lvm/lvm.conf:
>>>
>>>     auto_activation_volume_list = []
>>>
>>> 3. both 1 and 2
>>>
>>
>> I've now applied both of the above and regenerated the initramfs and
>> rebooted and the host no longer lists the LV's of the VM. Since I
>> rebooted the host before without this issue, I'm not sure a single
>> reboot is enough to conclude it has fully fixed the issue.
>>
>> You mention that there's no solution yet. Does that mean the above
>> settings are not 100% certain to avoid this behaviour?
>>
>> I was thinking of setting a global_filter in /etc/lvm/lvm.conf to only
>> include the PV's for the hypervisor disks (on which the OS is installed)
>> so the system lvm commands only touches those. Since vdsm is using its
>> own lvm.conf this should be OK for vdsm?
>
> This does not seem to work. The host can not be activated as it can't
> find his volume group(s). To be able to use the global_filter in
> /etc/lvm/lvm.conf, I believe it should be overridden in vdsm's lvm.conf
> to revert back to the default.
>
> I've moved my filter from global_filter to filter and that seems to
> work. When lvmetad is disabled I believe this should have the same
> effect as global_filter? The comments in /etc/lvm/lvm.conf indicate also
> udev might ignore the filter setting?

Right, global_filter exist so you can override filter used from the command
line.

For example, hiding certain devices from vdsm. This is why we are using
filter in vdsm, leaving global_filter for the administrator.

Can you explain why do you need global_filter or filter for the
hypervisor disks?

Do you have any issue with the current settings, disabling auto activation and
lvmetad?

Nir