Random failures were seen in XS attach/detach volume test scenarios (many attach/detach were performed on the same VM over a span of 24 hrs).
The failures happened as the device id for attaching volume wasn't available in HV. Some detached volume didn't got cleaned up properly and so the device id wasn't released.
The fix would be clean up stale volumes before attaching new ones so the device slots are released. Also using the device id should be best effort and if that particular id is not available in XS, it should fallback on using an id that is available and automatically assigned.