When Amazon notes "SSD," from a client's perspective, it is only marketing. The storage media matter when you are managing your own hardware. The storage media do not matter in SaaS. For example, the storage media could be floppys and you would get satisfactory performance if there was a memory cache. Similarly you could get poor performance with SSD media if the networking layer(s) were slow. Similarly if the storage media were fault-likely CD's that wouldn't matter either, to us, because of the data replication performed in "the service." What matters in this case is the reported and actual latency.