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

On 12/21/2011 05:41 PM, Daniel P. Berrange wrote: >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. I don't really understand. The host still scans the partitions, right? And the partition "dev" names change dynamically if the whole-disk changes it's "dev" name. Won't I still have to list specific volatile names in the /etc/lvm/lvm.conf on the host?