[saurik]

In the specific case of a database server that actually has correct fsync semantics that the user has not disabled for some crazy performance reason, you are correct. However, there are many use cases that people want consistent snapshots across, like "apt-get install", that do not use a write barrier for every atomic-feeling operation.

(In fact, with a good database solution, like PostgreSQL, the RAID issue of the parent post is also solved: put your write-ahead or checkpoint logs on a single device, as its linear writes will easily swamp network I/O on an EBS, and use RAID only for backend storage, where you need random I/O.)