Another thing to consider is that EBS offers snapshot backups and is therefore not functionally equivalent to the ephemeral disk which is not durable. Ephemera

Another thing to consider is that EBS offers snapshot backups and is therefore not functionally equivalent to the ephemeral disk which is not durable. Ephemeral disks offer more predictable performance, especially on the largest instances, however they will not provide the random iops of a raid set of EBS volumes.