[openstack-dev] Island: Local Storage Volume Support for Cinder

Rongze Zhu zrzhit at gmail.com
Thu Nov 8 03:14:10 UTC 2012


I am interested in how did you address the issues :)

On Tue, Nov 6, 2012 at 7:42 PM, John Garbutt <John.Garbutt at citrix.com>wrote:

> I am interested in following similar patterns with the XenServer SM work
> (for NFS and local volumes).
> We have the same issues around the hypervisor needing to be involved when
> taking a snapshot (but with VHDs in our case).
> https://blueprints.launchpad.net/cinder/+spec/xenapi-storage-manager
>
> We will try get back with some more concrete details once we sit down and
> flesh out the blueprint a bit more.
> We have done the prototyping to discover the issues now.
>
> John
>
> -----Original Message-----
> From: Christoph Hellwig [mailto:hch at infradead.org]
> Sent: 05 November 2012 11:38 AM
> To: OpenStack Development Mailing List
> Subject: Re: [openstack-dev] Island: Local Storage Volume Support for
> Cinder
>
> On Fri, Nov 02, 2012 at 03:54:02PM -0700, Vishvananda Ishaya wrote:
> > So we dealt with this exact issue when doing snapshots for instances.
> > According to the libvirt folks, creating and/or deleting a snapshot
> > using qemu-image while a disk is in use is not safe.
>
> It's indeed not.  Creating snapshots of any image format while qemu is
> running requires doing it using the qemu monitor.  Note that this is the
> exact same snapshot code that qemu-img would invoke, but doing it from qemu
> means it is serialized vs I/O from the guest.
>
> > Unfortunately libvirt does not expose a reasonable method for
> > snapshotting and extracting data from a live disk, so the only way to
> > do this safely is to use qemu-monitor (or patch libvirt to expose the
> > right interface). This is why the instance snapshot command in kvm is
> > doing a managed save before snapshotting the vm. If we had a good way
> > to do this it would greatly help the instance snapshot code as well.
>
> What do you mean with a managed save?
>
>
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Rongze Zhu - 朱荣泽
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