[jdunck]

And what happens when the AZ goes down? Don't you lose data then? Or do you mean multiple machines across AZ/region?

[joevandyk]

You'll want the mirror in a different AZ. Or you could also put it in a different region.

Use Wal-E to push wal logs to s3.

[bmurphy]

Absolutely. You should always be spreading your data across multiple availability zones and where feasible across multiple data centers and S3 is a great place to store your wal logs. We do the same thing.