On 06/16/2012 10:59 AM, Peter Eckel wrote:
> Hi Dennis,
>
>> The partitioning of the new disk in the guest is important because if you
>> use the disk directly as a PV then this PV will also be shown on the host.
>> An alternative is to modify the LVM filters in /etc/lvm/lvm.conf on the
>> host to specifically not scan the LV for the new disk.
>> I find it easier to create a partition though (i.e. use /dev/vda1 instead
>> of /dev/vda as the PV).
>
> Thanks for your explanation. Until now I just filteres the guests' PVs on the host on the "human interface level" by simply ignoring them, but yours is definitely the cleaner and more secure way.
>
> Maybe I missed something, but in what way is it easier to partition each and every LV one wants to use as a PV in a guest than to specify a proper filter in /etc/lvm/lvm.conf once?
>
> I use a consistent naming scheme for the lv's like
>
> /dev/vg_<number>/lv_virt_<hostname>
>
> and use the filter
>
> filter = [ "r|/dev/vg_\d+/lv_virt_\.*|" ]
>
> to ignore all the guest's PVs. Is there any downside in doing that, or are there any advantages in using partitions instead of raw 'devices' for the PVs?
I don't think there are any meaningful advantages or disadvantages to
either approach. The partition approach allows you to copy and use the
disks on any system regardless of the filter configuration because LVM can
never see the metadata directly but even then if you forget the filter this
just makes things look a bit untidy until the filter is in place.
Hopefully the new virtio-scsi driver will allow the on-the-fly resizing of
virtual disks and make the live extension of diskspace in virtual machines
less cumbersome.
Regards,
Dennis
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