Re: block snapshot issue with RBD

[Jin Cao]

Hi Ilya

On 5/28/24 11:13 AM, Ilya Dryomov wrote:
> On Mon, May 27, 2024 at 9:06 PM Jin Cao <jojing64@gmail.com> wrote:
> > Supplementary info: VM is paused after "migrate" command. After being
> > resumed with "cont", snapshot_delete_blkdev_internal works again, which
> > is confusing, as disk snapshot generally recommend I/O is paused, and a
> > frozen VM satisfy this requirement.
>
> Hi Jin,
>
> This doesn't seem to be related to RBD.  Given that the same error is
> observed when using the RBD driver with the raw format, I would dig in
> the direction of migration somehow "installing" the raw format (which
> is on-disk compatible with the rbd format).

Thanks for the hint.

> Also, did you mean to say "snapshot_blkdev_internal" instead of
> "snapshot_delete_blkdev_internal" in both instances?

Sorry for my copy-and-paste mistake. Yes, it's snapshot_blkdev_internal.

--
Sincerely,
Jin Cao

> Thanks,
>
>                  Ilya
>
> > --
> > Sincerely
> > Jin Cao
> >
> > On 5/27/24 10:56 AM, Jin Cao wrote:
> > > CC block and migration related address.
> > >
> > > On 5/27/24 12:03 AM, Jin Cao wrote:
> > > > Hi,
> > > >
> > > > I encountered RBD block snapshot issue after doing migration.
> > > >
> > > > Steps
> > > > -----
> > > >
> > > > 1. Start QEMU with:
> > > > ./qemu-system-x86_64 -name VM -machine q35 -accel kvm -cpu
> > > > host,migratable=on -m 2G -boot menu=on,strict=on
> > > > rbd:image/ubuntu-22.04-server-cloudimg-amd64.raw -net nic -net user
> > > > -cdrom /home/my/path/of/cloud-init.iso -monitor stdio
> > > >
> > > > 2. Do block snapshot in monitor cmd: snapshot_delete_blkdev_internal.
> > > > It works as expected: the snapshot is visable with command`rbd snap ls
> > > > pool_name/image_name`.
> > > >
> > > > 3. Do pseudo migration with monitor cmd: migrate -d exec:cat>/tmp/vm.out
> > > >
> > > > 4. Do block snapshot again with snapshot_delete_blkdev_internal, then
> > > > I get:
> > > >      Error: Block format 'raw' used by device 'ide0-hd0' does not
> > > > support internal snapshots
> > > >
> > > > I was hoping to do the second block snapshot successfully, and it
> > > > feels abnormal the RBD block snapshot function is disrupted after
> > > > migration.
> > > >
> > > > BTW, I get the same block snapshot error when I start QEMU with:
> > > >       "-drive format=raw,file=rbd:pool_name/image_name"
> > > >
> > > > My questions is: how could I proceed with RBD block snapshot after the
> > > > pseudo migration?