After a power failure of the host machine, the openstack cinder volumes have entered a state in which they can not be attached nor detached.
~$ nova volume-attach ### ###
ERROR: Invalid volume: already attached (HTTP 400) (Request-ID: req-###)
~$ nova volume-detach ### ###
ERROR: Invalid volume: already detached (HTTP 400) (Request-ID: req-###)
The status of the volume its self is listed as attached
cinder list
+-----+-----------+---------------------+------+-------------+----------+-------------+
| ID | Status | Display Name | Size | Volume Type | Bootable | Attached to |
+-----+-----------+---------------------+------+-------------+----------+-------------+
| ### | available | volume-data | 690 | Storage | false | ### |
+-----+-----------+---------------------+------+-------------+----------+-------------+
The volume is not found on the instance even though its listed as attached in the cli and in horizon (the device isnt found in /dev/ nor the mount point in /mnt/)