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Re: [libvirt-users] Can I move the disk image of the guest while it is running?




----- Original Message -----
> From: "Eric Blake" <eblake redhat com>
> To: "Andrew Martin" <amartin xes-inc com>
> Cc: "Gergely Horváth" <gergely horvath inepex com>, libvirt-users redhat com
> Sent: Thursday, February 6, 2014 2:35:35 PM
> Subject: Re: [libvirt-users] Can I move the disk image of the guest while it is running?
> 
> On 02/06/2014 01:25 PM, Andrew Martin wrote:
> > ----- Original Message -----
> >> From: "Eric Blake" <eblake redhat com>
> >> To: "Andrew Martin" <amartin xes-inc com>
> >> Cc: "Gergely Horváth" <gergely horvath inepex com>,
> >> libvirt-users redhat com
> >> Sent: Thursday, February 6, 2014 9:31:29 AM
> >> Subject: Re: [libvirt-users] Can I move the disk image of the guest while
> >> it is running?
> >>
> >> On 02/06/2014 08:14 AM, Andrew Martin wrote:
> >>> Eric,
> >>>
> >>> For scripted live backups, which non-transient technique would you
> >>> prefer:
> >>> 1. snapshot-create-as followed by blockpull, which results in the
> >>> original
> >>> file being left as a standalone copy of the VM from that point in time;
> >>> it
> >>> can then be copied off to a backup disk once blockpull completes
> >>
> >> Slower (because it pulls the entire contents of the original file into
> >> the new file), but likely to succeed.
> > Is there a faster, non-transient way to do this with the current versions
> > of qemu and libvirt?
> 
> Sadly, no.  The whole area of block chain management is still undergoing
> active development, and qemu 2.0 definitely adds some nice features to
> the mix that libvirt will have to be taught to support.
> 
> > 
> >>
> >>> 2. snapshot-create-as followed by copying the backing file (since it is
> >>> now
> >>> read-only) and then using blockcommit to pull the interim changes back
> >>> into
> >>> the original/backing file (and removing the snapshot file)
> >>
> >> Ideal, but not supported until (unreleased) qemu 2.0.
> >>
> > Ah, does blockcommit currently only work with offline VMs with qemu 1.x?
> 
> Blockcommit does not yet work with offline VMs.  But you can get the
> same behavior as what offline blockcommit would do by using qemu-img
> manually.  One idea for a patch is to see if 'qemu -M none' can drive a
> block commit operation using a long-running qemu process that does
> nothing but the block operation; if that works, then we could wire up
> libvirt to do long-running block operations that survive a libvirtd
> restart.  But the reason libvirt doesn't currently support offline
> operations is that we have no way to keep a long-running qemu-img
> operation running smoothly across a libvirtd restart.
Thanks for the clarification!

Andrew



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