Re: block snapshot issue with RBD

[Ilya Dryomov]

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).

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

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?