Ordinarily, Cinder volumes can only be attached to one instance at a time. Thus, you need to detach it from one instance before attaching it to another. To detach a volume, we will use another OpenStack client command called openstack server remove volume.
To detach a volume from an instance, you will need the following:
- The
openstackcommand-line client - An
openrcfile with appropriate credentials for the environment - The name or ID of the volume to detach
- The name or ID of the instance to detach the volume from
For our example, these values are as follows:
- Volume:
cookbook.volume - Instance:
cookbook.test - Mount point:
/mnt1
Carry out the following steps to detach a volume to an instance using the openstack client:
- List running instances to get the ID of our instance:
- List the volumes that are available and
in-usein our environment:openstack volume listThis will bring back an output like the following. Note that the information provided shows you if a volume is in use and what instance it is attached to:
- We now need to perform actions inside the running instance. Connect to this instance and verify that the volume is mounted:
df -hThis will show an output like the following:
Filesystem Size Used Avail Use% Mounted on udev 238M 0 238M 0% /dev tmpfs 49M 1.8M 48M 4% /run /dev/vda1 2.1G 843M 1.3G 41% / tmpfs 245M 0 245M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 245M 0 245M 0% /sys/fs/cgroup tmpfs 49M 0 49M 0% /run/user/1000 /dev/vdb 9.8G 23M 9.2G 1% /mnt1
- Now unmount the
/mnt1volume:sudo umount /mnt1(Verify that it has been unmounted by running
df -hagain). - Exit the guest, and back on our OpenStack client, detach the volume from the instance with the following command:
openstack server remove volume cookbook.test c ookbook.volume
- This command doesn't produce any output on success, so view the volume list again to verify that the volume has been detached from the
cookbook.testinstance:openstack volume listThis shows the volume is available and not attached to any instance:
Detaching a Cinder volume from an instance is similar to the steps you would take when removing a USB stick from a computer. First, we need to unmount it from the instance so the operating system doesn't complain about an unexpected removal of some storage. Next under the openstack client, the server remove volume option takes the following syntax:
openstack server remove volume instance_name_or_id volume_name_or_id