I reproduced it with StarlingX. After the initial cold migration we're left with this on the original compute node:
compute-1:~$ ls -l /var/lib/nova/instances/
total 36
drwxr-xr-x 2 root root 4096 Jun 19 23:15 _base
-rw-r--r-- 1 root root 32 Jun 19 22:51 compute_nodes
drwxr-xr-x 2 root root 4096 Jun 19 23:19 fba5ba3d-c515-4b5f-aecd-8b9137dcddae
drwxr-xr-x 2 root root 4096 Jun 19 23:15 fba5ba3d-c515-4b5f-aecd-8b9137dcddae_resize
drwxr-xr-x 2 root root 4096 Jun 19 23:15 locks
drwx------ 2 root root 16384 Jun 19 15:08 lost+found
compute-1:/var/lib/nova/instances$ ls -l fba5ba3d-c515-4b5f-aecd-8b9137dcddae
total 0
compute-1:/var/lib/nova/instances$ ls -l fba5ba3d-c515-4b5f-aecd-8b9137dcddae_resize
total 96
After confirming the migration, the "_resize" directory was deleted.
Looking at the timestamps, it appears that something is re-creating the instance directory after it's been renamed.
I reproduced it with StarlingX. After the initial cold migration we're left with this on the original compute node:
compute-1:~$ ls -l /var/lib/ nova/instances/ c515-4b5f- aecd-8b9137dcdd ae c515-4b5f- aecd-8b9137dcdd ae_resize
total 36
drwxr-xr-x 2 root root 4096 Jun 19 23:15 _base
-rw-r--r-- 1 root root 32 Jun 19 22:51 compute_nodes
drwxr-xr-x 2 root root 4096 Jun 19 23:19 fba5ba3d-
drwxr-xr-x 2 root root 4096 Jun 19 23:15 fba5ba3d-
drwxr-xr-x 2 root root 4096 Jun 19 23:15 locks
drwx------ 2 root root 16384 Jun 19 15:08 lost+found
compute- 1:/var/ lib/nova/ instances$ ls -l fba5ba3d- c515-4b5f- aecd-8b9137dcdd ae 1:/var/ lib/nova/ instances$ ls -l fba5ba3d- c515-4b5f- aecd-8b9137dcdd ae_resize
total 0
compute-
total 96
After confirming the migration, the "_resize" directory was deleted.
Looking at the timestamps, it appears that something is re-creating the instance directory after it's been renamed.