----- Original Message ----- > From: "Stefan Hajnoczi" <stefa...@gmail.com> > To: "Federico Simoncelli" <fsimo...@redhat.com> > Cc: qemu-devel@nongnu.org, kw...@redhat.com, mtosa...@redhat.com > Sent: Thursday, February 23, 2012 4:47:38 PM > Subject: Re: [Qemu-devel] Live Block Migration using Mirroring > > On Wed, Feb 22, 2012 at 5:13 PM, Federico Simoncelli > <fsimo...@redhat.com> wrote: > > Step 3 - Mirrored Live Snapshot > > =============================== > > A mirrored live snapshot is issued using src/hd0snap1 and > > dst/hd0snap1 as > > image files. (Where "<-" stands for "has backing file") > > > > [src/hd0base] <- [src/hd0snap1] <= VM1(read-write) > > ... <- [dst/hd0snap1] <= VM1(write-only) > > > > $ qemu-img create -f qcow2 \ > > -b /tmp/src/hd0base.qcow2 /tmp/src/hd0snap1.qcow2 20G > > Formatting '/tmp/src/hd0snap1.qcow2', fmt=qcow2 size=21474836480 > > backing_file='/tmp/src/hd0base.qcow2' encryption=off > > cluster_size=65536 > > > > $ qemu-img create -f qcow2 \ > > -b /tmp/dst/hd0base.qcow2 /tmp/dst/hd0snap1.qcow2 20G > > Formatting '/tmp/dst/hd0snap1.qcow2', fmt=qcow2 size=21474836480 > > backing_file='/tmp/src/hd0base.qcow2' encryption=off > > cluster_size=65536 > > At this stage /tmp/dst/hd0base.qcow2 does not exist yet. The > qemu-img > output you pasted shows /tmp/src/hd0base.qcow2 was actually used. > Typo?
No that's part of the flag used in [PATCH 2/3] (Update the blkmirror block driver): BDRV_O_NO_BACKING It's also documented in the design: http://www.ovirt.org/wiki/File:StorageLiveMigration2.png > > (qemu) snapshot_blkdev -n ide0-hd0 \ > > blkmirror:/tmp/src/hd0snap1.qcow2:/tmp/dst/hd0snap1.qcow2 > > blkmirror > > > > Step 4 - Backing File Copy > > ========================== > > An external manager copies src/hd0base to the destination > > dst/hd0base. > > > > [src/hd0base] <- [src/hd0snap1] <= VM1(read-write) > > [dst/hd0base] <- [dst/hd0snap1] <= VM1(write-only) > > > > $ cp -a /tmp/src/hd0base.qcow2 /tmp/dst/hd0base.qcow2 > > Are we missing a fixup step that changes backing_file in > dst/hd0snap1.qcow2 to point at dst/hd0base.qcow2? See above. -- Federico
