[pve-devel] [PATCH v4 qemu-server 2/2] remote-migration: add target-cpu && target-reboot params

[DERUMIER, Alexandre]

Hi Fiona,


>>In case of 'restart' migration, we do want to start the VM anyways,
>>so
>>it's actually better, because we can catch config issues early :) Now
>>that I think about it, can we also just start the target VM in
>>prelaunch
>>mode (instead of incoming migration mode), do the NBD migration, shut
>>down the source VM, stop the NBD server and then resume the target?
>>That
>>would avoid the need to stop and start the target again. And
>>therefore
>>might be quite a bit less downtime.


I have done some tests, It's not possible currently to write to the
remote nbd without the --incoming migration flag and only -S



https://lists.gnu.org/archive/html/qemu-devel/2017-11/msg05700.html



nbd_add is throwing an error like

2023-10-23 18:45:51 [formationkvm1] VM 111 qmp command 'block-export-
add' failed - Permission conflict on node '#block524': permissions
'write' are both required by an unnamed block device (uses node
'#block524' as 'root' child) and unshared by block device 'drive-scsi0'
(uses node '#block524' as 'root' child).


Looking at the qemu code, the are some specific codepath in block when
the incoming flag is setup.


So I think the best way for now is to restart the target vm.