Re: Migration issue - disk image was not updated.

[Avi Kivity <avi@redhat.com>]

On 07/18/2011 05:39 PM, Stefan Hajnoczi wrote:
> On Mon, Jul 18, 2011 at 2:08 PM, sirmax<sirmax@noname.com.ua>  wrote:
> >  Node B with VM started:
> >
> >  VM_IMAGE="/usr/local/virtual/img/win-xp-test-migrate.img"
> >  VM_NAME="win-xp-test-m"
> >  DEV0="kvm_m1"
> >
> >  TMPDIR="/var/tmp/"  /usr/bin/kvm \
> >      -hda $VM_IMAGE \
> >      -net nic -net tap,ifname=${DEV},script=no,downscript=no \
> >      -boot c \
> >      -vnc :15 \
> >      -usbdevice tablet \
> >      -usb \
> >      -snapshot \
> >      -monitor tcp:127.0.0.1:4415,server,nowait \
> >      -monitor unix:/tmp/${VM_NAME}.fifo,server,nowait \
> >      -incoming tcp:172.16.253.1:9999
>
> The -snapshot command works by creating a temporary qcow2 image file
> based on the disk image.  In your case the effect is something like:
> qemu-img create -f qcow2 -o backing_file=$VM_IMAGE /tmp/...
>
> This temporary file is now your disk image.  All write operations from
> the guest will touch the temporary file and *not* the base image
> ($VM_IMAGE).
>
> When you combine -snapshot with live migration QEMU creates the
> temporary image before performing the block migration.  Therefore the
> block migration copies over all data into the temporary file (doh!).
>
> Seems like a special case to me that would need to be carefully fixed
> by performing snapshotting after block migration.
>

Why?  It seems to me -snapshot means "don't write into this image".

What I'd expect is that all data be written into the temporary image, 
perhaps with the optimization that unchanged data is taken from the 
backing file.

-- 
error compiling committee.c: too many arguments to function