[openstack-dev] [nova][cinder][libvirt] Serious problem of block migration of a hybrid instance (instance based on local disk and cinder volume attached)

Luo Gangyi lgy181 at foxmail.com
Wed May 20 10:11:26 UTC 2015


Hi devs,


I find a serious problem when I try to live migrate a hybrid instance (instance based on local disk and cinder volume attached) .


In current nova, such operation is allowed.


But I don't think libvirt can deal with such condition correctly.


When block migration of a hybird intance is triggered, nova will initiate a new connection to the volume in destination compute node and then
call libvirt to do the block migration.


However, libvirt doesn't distinguish local disk and a network volume, it may copy both local disk and cinder volume from source to destination.


It is dangerous  to write the same volume simutaneously on source and destination!! and apparently there is no need to do this!




I believe we should do something to correct this, maybe patch libvirt? or just forbid user do such operation?


------------------
Luo Gangyi
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