Re: [libvirt] [PATCH 0/5]Add startupPolicy attribute support for hard disks

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