Also, we tried to take snapshot at t,t+1,t+2 times when writing data all times. Snapshots is successfully but when we rescue instance, the process wasn't success.

Openstack Horizon Output:  Error: Unable to rescue instance Details Requested rescue image 'ddc2df28-4f5-434b-9f9a-030e56425fc5' is not supported (HTTP 400) (Request-ID: req-065126c2-7f5f-4fd0-81b0-b45df446a83b)

Nova-Api Log File : Unable to rescue an instance using a volume snapshot image with img_block_device_mapping image properties set

Snapshot has already snapshot volume id in block_device_mapping metadata field. We are using Ceph for block storage. Is it related this issue ?