OpenStack – Detaching volumes from an instance
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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.
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:
sudo apt-get update
sudo apt-get install python-novaclient
How to do it…
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:
nova volume-detach <instance_id> <volume_id>
- We are now free to attach this to another running instance, with data preserved.
How it works…
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.