Re: [Qemu-devel] Qemu migration with vhost-user-blk on top of local storage

[Stefan Hajnoczi]

On Wed, Jan 09, 2019 at 06:23:42PM +0800, wuzhouhui wrote:
> Hi everyone,
> 
> I'm working qemu with vhost target (e.g. spdk), and I attempt to migrate VM 
> with
> 2 local storages. One local storage is a regular file, e.g. /tmp/c74.qcow2, 
> and
> the other is a malloc bdev that spdk created. This malloc bdev will exported 
> to
> VM via vhost-user-blk. When I execute following command:
> 
>   virsh migrate --live --persistent --unsafe --undefinesource 
> --copy-storage-all \
>      --p2p --auto-converge --verbose --desturi qemu+tcp://<uri>/system vm0
> 
> The libvirt reports:
> 
>   qemu-2.12.1: error: internal error: unable to execute QEMU command \
>     'nbd-server-add': Cannot find device=drive-virtio-disk1 nor \
>     node_name=drive-virtio-disk1

Please post your libvirt domain XML.

> Does it means that qemu with spdk on top of local storage don't support 
> migration?
> 
> QEMU: 2.12.1
> SPDK: 18.10

vhost-user-blk bypasses the QEMU block layer, so NBD storage migration
at the QEMU level will not work for the vhost-user-blk disk.

Stefan

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