When running on EC2, you often can't win when it comes to instance types. One of the more cost-effective types available is the c1.xlarge. It has enough CPU to handle compactions, a decent amount of disk, and high network I/O. However, we've found that the relatively low memory of 7GB on the c1.xlarge often leads to stability issues in highly concurrent HBase clusters. While there are other more expensive options, this HBase tutorial will help you make the most of your c1.xlarge RegionServers.