I have the following topology

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

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.