Re: block snapshot issue with RBD

[Jin Cao <jojing64@gmail.com>]

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?