Since Cinder Volumes are persistent storage and the best way of thinking of them is as a USB drive, this means that you can only attach them to a single computer at a time. When you remove a USB drive from the computer, you can then move it to another one and attach it. The same principle works with Nova Volumes. To detach a volume, we use another Nova Client option volume-detach.
How to detach Volume from an Instance
To begin with, ensure you are logged into the Ubuntu client that has access to Nova Client tools. These packages can be installed using the following commands:
Steps to detach a volume using Nova client
Carry out the following steps to detach a volume using Nova Client:
- First, we identify the volumes attached to running instances, by running the command nova volume-list, as follows:
- This brings back the following output:
- On the instance that has the volume mounted, we must first unmount it as follows (if using the example before, this is on /mnt1):
sudo unmount /mnt1
- Back on the Ubuntu client, where Nova Client is installed, we can now detach this volume as follows:
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- We are now free to attach this to another running instance, with data preserved.
Detaching Cinder Volume
Detaching cinder-volume is no different from removing a USB stick from a computer. We first unmount the volume from our running instance. Then, we detach the volume from the running instance using nova volume-detach from Nova Client.
nova volume-detach has the following syntax:
nova volume-detach instance_id volume_id
instance_id is the ID from the Attached to column returned from nova volume-list for the instance we want to detach the volume from volume id column from the nova volume-list command.
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