A storage volume is a virtual disk that provides persistent block storage space for instances in Oracle Compute Cloud Service. You can use storage volumes to store data and applications.
You can attach one or more storage volumes to an instance either while creating the instance or later when the instance is running. After creating an instance, you can easily scale up or scale down the storage resource for the instance by attaching or detaching storage volumes. However, you cannot detach a storage volume that was attached during instance creation. Note that, when a storage volume is detached from an instance or when the instance is deleted, data stored on the storage volume is not lost.
You can also take snapshots of the storage volumes at any time. See About Snapshot of Storage Volumes.
A snapshot is a copy made of the storage volume at any instant. A snapshot of a storage volume is another storage volume.
When you want to attach the storage volume to an running instance, you can back up the original volume by taking the snapshot of it.
When a storage volume is attached to a running instance and is running out of space. You can take a snapshot of the storage volume with an increased size of the volume. Then, you can attach the new storage volume and detach the old storage volume.