Migration issue - disk image was not updated.

Migration issue - disk image was not updated.

[sirmax]

Hi!

I have the following issue during live migration without shared storage:

Node A with VM  started:

VM_IMAGE="/usr/local/virtual/img/win-xp-test-migrate.img"
VM_NAME="win-xp-test-m"
DEV0="kvm_m1"

/usr/bin/tunctl -b -u root -t ${DEV0}
/sbin/ifconfig  ${DEV0} up
screen -dmS $VM_NAME \
     TMPDIR=/var/tmp/ /usr/bin/kvm \
     -hda $VM_IMAGE \
     -net nic -net tap,ifname=${DEV0},script=no,downscript=no \
     -boot c \
     -vnc :15 \
     -usbdevice tablet \
     -usb \
     -monitor tcp:127.0.0.1:4415,server,nowait \
     -monitor unix:/tmp/${VM_NAME}.fifo,server,nowait


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

When I tried to migrate VM from Node A to node B with the following 
command: migrate -d -b tcp:172.16.253.1:9999 
migration was completed w/o errors, but VM started on node B
did not see disk ${VM_IMAGE}

As I can see using lsof tool, disk was migrated into tmp file 
/var/tmp/vl.75BIcF :

lsof
<skipped>
qemu-syst 21377 root   11u   REG                9,3 21478375424   4057182 
/var/tmp/vl.75BIcF (deleted)


and  ${VM_IMAGE} was not updated


Could you please explain me what is wrong in my configuration?

Regrads,

----------------------------------------------------------
Max Mazur



                                Email:   sirmax@noname.com.ua
                                ICQ:     99610406

Re: Migration issue - disk image was not updated.

[Stefan Hajnoczi]

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.

Stefan

Re: Migration issue - disk image was not updated.

[Avi Kivity]

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

Re: Migration issue - disk image was not updated.

[sirmax]

On Mon, 18 Jul 2011, Avi Kivity wrote:

> 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

Thanks a lot for your help!

After I've removed "-snapshot" live migration was sucessfully finished!
VM migarted with about only 0.8 sec network downtime while switch re-learned 
MAC-address on new port.


Regards,
-------
Max Mazur.