Amazon Elastic Block Storage (EBS) is a new type of storage designed specifically for Amazon EC2 instances. Amazon EBS allows you to create volumes that Amazon EC2 instances can mount as devices much like a standard hard drive.
Amazon EBS volumes behave like raw unformatted external block devices. They have user-supplied device names and provide a block device interface. You can load a file system on top of Amazon EBS volumes, or use them just as you would use a block device.
For example : you can attach as /dev/sdj and later on format and mount it . see here
Since EBS Volumes behave just like any other mounted hard drive you can do anything with them you would do with standard hard drives, even make a RAID array
Amazon EBS volumes can now be used as the root device for an instance. These instances launch faster, use persistent storage, and support larger root device sizes than AMIs that use the local instance store as their root device. For more information, go to the Amazon Elastic Compute Cloud Developer Guide or the Amazon Elastic Compute Cloud User Guide.