On Tue, Mar 19, 2013 at 03:56:40PM +0800, Guannan Ren wrote: > On 03/18/2013 10:42 PM, Daniel P. Berrange wrote: > >On Mon, Mar 18, 2013 at 05:10:17PM +0800, Guannan Ren wrote: > >>The set of patches is trying to add 'startupPolicy' attribute support > >>to the source element of hard disks. Policy levels are using the > >>mandatory, requisite, optional levels as originally documented. > >> > >>For the 'optional' policy, there is a little difference from CDROM and > >>Floppy which only drop its source path, for disks, if missing, the > >>checking function will drop their definitions, because qemu doesn't > >>allow missing source path for hard disk. > >What is the motivation for this feature ? I personally find even the > >existing CDROM code for this to be of rather dubious value, so would > >like to see a clear use case for why we need to expand this hack. > > > >Daniel > > There is a real case from a libvirt customer request, which needs > to make disk of block type use "optional" policy. > > "The DR concept for our virtualization infrastructure is based upon > host-based mirroring of independent SAN LUNs. > Because RH does not support CLVM spanning multiple data centers > we have to pass the LUNs to the KVM and mirror inside of the KVM. > If there is an outage taking down a storage box or an entire DC, > we will be unable to migrate, relocate or start any KVM, > despite the KVM being able to run just on one side of the mirror." > > "Declare all devices as optional. If there aren't any mirror > parts left, > the KVM will fail, but that is an acceptable behaviour that will be > recognized by our monitoring software. There is no need to have > libvirt guard against failure of storage devices in such a setup. " Ok, so they are doing multi-pathing inside the guest, and so don't care if some of the LUNs on the host are not available when started. This makes more sense now as a feature. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list