Will a SSD storage perform like a magnetic for small root volumes in AWS EC2?
You forgot the burst capacity. For both EBS magnetic and General purpose SSD, the "base" speed is as you said. Base speed is the minimuum guaranteed speed in any moment. But, while with magnetic disks you have a burst capacity of a "few hundreds", with SSD you can go up to 3000 iops. It then depends on what use you make of your machine: need stable constant i/o performance on a small disk through the whole day? Go magnetic. Have the casual I/O spike (reboots, a few minutes of heavy traffic, your night backup process)? Perfect scenary for the general purpose SSD.