Amazon Rds m4 VS m3, which is better

Question

I looked here: https://aws.amazon.com/rds/pricing/

It's seems like amazon rds M4 Is better and cheaper then M3, It's doesnt makes sense to me.

Why would anyone want to use M3

Answer 1

The M3s are the previous generation, and as you correctly note are slower and more expensive, therefore if you were starting up a new RDS instance the obvious choice would be M4. However M4s are not available in all regions yet (South America being the one remaining region offering only M3s.)

(It also makes sense to continue displaying pricing for users still running M3 instances.)

Answer 2

M4 have no local instance storage, so you have to pay (in terms of delay) for network traffic for all disk writes, which slows up things that could be much faster with instance store, such as paging file, SQL Server temp databases, etc.