On 4/8/13 4:19 PM, "Marcus Sorensen" <shadow...@gmail.com> wrote:
>Oh yes, I know these things, but here's my point. You said: > >"When CloudStack takes a snapshot of volume, it already utilizes snapshot >feature provided by hypervisor to allow taking point of time storage image >in a safe manner from operating system point of view." > >What about five volumes? Can we ensure they are all snapshotted at that >same point in time without also pausing the VM, in addition to using those >hypervisor-provided features? For example, let's say the VM is using a >volume manager and striping data across five data disks, we absolutely >have >to take all data disk snapshots at the same point in such a scenario. We >of >course have to rely on the user to tell us that they want this, but we >should have the capability. > >If we already have a VM snapshot feature that does every connected disk >simultaneously while the VM is suspended, or the hypervisor can do it for >us by quickly pausing/snapshotting/resuming seamlessly then fine, that's >great. It just didn't seem like that functionality existed now, so I was >wondering if anyone is working on it. I'm not sure using the tactic to pause a VM for the purpose of ensuring full data integrity is the right answer for the use case you pointed. As far as I know for VMware hypervisors, taking a VM snapshot does all the things your mentioned above (quiesce the guest file system, snapshot memory etc). Xen Server may be a little different, for crash consistency, I think we ask user to stop a VM(instead of pausing it) before taking a volume snapshot. So the question is, can "pausing VM" offer what we are looking for or is it a half-completed solution? Forcely-pausing a VM to offer a not ensured solution to customer is what I'm worrying about. -Kelven > >That aside, it seems like all of the hypervisors CS controls provide their >own UI to pause a VM. Is it something that has been discussed? > > > > >On Mon, Apr 8, 2013 at 4:16 PM, Kelven Yang <kelven.y...@citrix.com> >wrote: > >> >> >> On 4/8/13 1:39 PM, "Marcus Sorensen" <shadow...@gmail.com> wrote: >> >> >Has anyone put together a suggestion for adding a 'paused' state to >> >virtual >> >machines? Or is anyone working on it? This seems fairly >>straightforward, >> >and I think we may need the functionality going forward. Even if people >> >rarely use it themselves, if storage solutions are going to offer >> >snapshots >> >they may want to pause the VM in order to get an atomic snapshot if >>the VM >> >has multiple disks. So at least internally it may be a useful utility. >> >> Pause VM itself can not ensure data integrity. True data integrity can't >> be ensured without participant of guest OS and related application (for >> example, Microsoft offers Volume Shadow Copy Service to orchestrate and >> allow applications to participate the process via a set of tools and API >> interaction to achieve that). >> >> When CloudStack takes a snapshot of volume, it already utilizes snapshot >> feature provided by hypervisor to allow taking point of time storage >>image >> in a safe manner from operating system point of view. The ability of >> pausing VM is not mandatory in this case, although pausing/resuming VM >>may >> be useful in certain use case, it does not seem to be in any urgency or >> fit naturally in general cloud-operations. >> >> -Kelven >> >> > >> >>
