Explanation: io1 volumes, or Provisioned IOPS (PIOPS) SSDs, are best for: Critical business applications that require sustained IOPS performance, or more than 10,000 IOPS or 160 MiB/s of throughput per volume, like large database workloads, such as MongoDB.
Reference:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSVolumeTypes.html