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

[Guannan Ren]

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. "

      https://bugzilla.redhat.com/show_bug.cgi?id=910171

      Guannan