I have the following topology

    City 1                                                City 2
    Master <----> Distribution Master (EC2 Instance) <---> Slave

* Master : Write heavy
* Distribution Master: Read only
* Slave: Read only

There won't be any application in front of Distribution Master.

Distribution Master is slave of Master and Master of SlaveServer
. Master and Slave are in different cities and the replication needs to be Asynchronous.

The EC2 instance just gets the data from Master and replicates to the Slave when a connection is established. 

* Do you think I need SSD volumes for the Replication Master? 
* Or will a cold HDD (sc1) will be enough? 

With a cold storage solution I can get more space for a much lower price.