Amazon Elastic Block Store (Amazon EBS) provides block-level storage volumes for use with EC2 instances. EBS volumes behave like raw, unformatted block devices. You can mount these volumes as devices on your instances.
You can mount multiple volumes on the same instance, but each volume can be attached to only one instance at a time.
You can create a file system on top of these volumes, or use them in any way you would use a block device (like a hard drive). You can dynamically change the configuration of a volume attached to an instance