You can attach a volume to a guest VM to provide extra disk storage. Attach a volume when you first create a new volume, when you are moving an existing volume from one VM to another, or after you have migrated a volume from one storage pool to another.
Log in to the CloudStack UI as a user or admin.
In the left navigation, click Storage.
In Select View, choose Volumes.
4. Click the volume name in the Volumes list, then click the Attach Disk button
In the Instance popup, choose the VM to which you want to attach the volume. You will only see instances to which you are allowed to attach volumes; for example, a user will see only instances created by that user, but the administrator will have more choices.
If the VM is running in the OVM hypervisor, the VM must be stopped before a new volume can be attached to it.
When the volume has been attached, you should be able to see it by clicking Instances, the instance name, and View Volumes.