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

On 12/22/2011 12:44 PM, Daniel P. Berrange wrote: > On Thu, Dec 22, 2011 at 09:20:01AM -0500, David Mansfield wrote: >> >> 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? > The host will see '/dev/sda' and '/dev/sda1', you'll assign > ' /dev/sda1' to the guest, and it will appear as /dev/vda. > In the guest you'll create '/dev/vda1' and format it as the > PV. So while the host will see /dev/sda1, it won't see the > nested partition table, and thus won't see the PV Ahhh. Brilliant. Thanks. Now the only problem is getting the underlying stripe alignment right ;-)