OpenStack Cinder Metadata: attached-mode and readonly

When you attach a volume to an instance, Cinder automatically adds the attached_mode and readonly
key-value pairs to the volume. These tags describe the state of the volume and are not directly modifiable by the user.

The attached_mode key describes whether the volume is read-only or read-writable and appears only when the volume is attached.

The readonly key describes whether the volume can be attached as read-only or read-writeable .

Cinder automatically removes the attached_mode key when the volume is detached from an instance. However, the readonly key stays indefinitely.

To attach a volume as read-only,  set the read-only mode to true using the Cinder client:

cinder readonly-mode-update true

To attach as volume as read-writeable, set the read-only mode to false:

cinder readonly-mode-update false