The problem is that DB application will try to sync disk either via fsync or o_direct. EBS may have a very long latency for such kind access.

I'm just pointing out that you don't want to run your db on non-redundant disk. Really, I think in-ram, redundant databases like MySQL cluster are more suited to the 'cloud' - especially as you can get cheap ram.

Just looking at the bonnie results, ebs wasn't that far off everything else in terms of sequential access.