Quote Originally Posted by manteshpatil View Post

for instance 9b8289e2-c5d6-4003-9202-91e452e65738. Last exception:
Unexpected error while running command. Command: rbd import --pool nova //var/lib/nova/instances/_base/cfe43c0bc7cc07].
This "rbd" (Rados Block Device) indicates trouble with the ceph storage backend. Please check "ceph status"

If it says
health HEALTH_ERR

then you need to investigate there.

otherwise /var/log/nova/nova-scheduler.log might have more hints.

In general, the horizon dashboard always uses the nova API, so if one consistently works and the other does not, it is because the API calls are different. E.g. it can matter if you have the OS on volumes or on local ephemeral disks. You can try variations there to see which part matters.