[bmurphy]

EBS is a shared networked SAN. The performance characteristics of it are not that great and even worse, highly variable. The last thing you want to be running your database on is a system where the performance characteristics vary greatly throughout the day and you have no control over it.

The ephemeral drives are drives directly attached to the server and to the best of my knowledge are not a shared resource. Their performance characteristics are highly consistent, but if your server goes down all data on those drivers are lost.

EBS sounds nice in theory, but by going to EBS RAID you throw away most of its benefits (such as snapshotting) and take on it's worst aspects.

[alnayyir]

Ephemeral volumes are shared, just not nearly as variable.