Re: [libvirt-users] for a guest accessing host "full disk", how to prevent host vgscan

On Wed, Dec 21, 2011 at 05:23:33PM -0500, David Mansfield wrote: > Hi All. > > I have a dell system with a H700 raid. Within the hardware RAID > config I've created a "virtual disk" which I have assigned to one of > my guests. On the host the device is "/dev/sdb", on the guest it's > "/dev/vdb". > > This works fine. > > Within the guest, we have created lvm PV on /dev/vdb (using the > whole disk - no partitions) and created a volume group. The guest's > hostname is "argo" and the vg is called "vg_argo_bkup". > > When I reboot the host, it does a vgscan and finds the volume group > and activates it in the _host_, which I need to prevent (I think??). > > I have successfully done this by filtering "/dev/sdb" in > /etc/lvm/lvm.conf (which does NOT work as advertised BTW), but > referencing the extremely volatile SCSI "sd*" names seems a terrible > way to do this. If I fiddle around in the HW raid config, the > /dev/sd? may change. > > I plan on creating about 10 more VM's spread over a number of > machines over the next weeks with a very similar setup, and the > admin overhead seems like it'll be onerous and error-prone. > > I'd love to be able to filter the volume groups by VG name instead > of pv device node. The host's hostname is "narnia" and I'd love to > say, 'vgscan --include-regex "vg_narnia.*"' or something similar, if > you get my drift. > > Does anyone have a best practice for this? I'm sure iSCSI > enthusiasts must have the exact same issue all the time. The recommended approach is not to assign the entire disk to the guest. Partition the host disk, to contain 1 single partition consuming all space, then assign the partition to the guest. Worst case is you loose a few KB of space due to partition alignment, but this is a small price to pay to avoid the LVM problems you describe all to well.