We still use EBS for database backups via ec2-consistent-snapshot. The slave DB that performs this is not production-facing.

We have 2 separate chef recipes for our DBs:

One is for a full-time slave. This recipe will set up the db to use the EBS volume.

The other is for a slave that will be promoted to a master. In this case, we do a little extra legwork to do a bit-by-bit copy of a recent EBS snapshot, onto the ephemeral disk.

Sounds like I have more blog posts to write!