Re: block snapshot issue with RBD

[Jin Cao]

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.

--
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?