An Amazon EBS–optimized instance uses an optimized configuration stack and provides additional, dedicated capacity for Amazon EBS I/O. This optimization provides the best performance for your EBS volumes by minimizing contention between Amazon EBS I/O and other traffic from your instance.
EBS–optimized instances deliver dedicated bandwidth to Amazon EBS, with options between 500 Mbps and 10,000 Mbps, depending on the instance type you use. When attached to an EBS–optimized instance, General Purpose SSD (gp2) volumes are designed to deliver within 10% of their baseline and burst performance 99% of the time in a given year, and Provisioned IOPS SSD (io1) volumes are designed to deliver within 10% of their provisioned performance 99.9% of the time in a given year. Both Throughput Optimized HDD (st1) and Cold HDD (sc1) guarantee performance consistency of 90% of burst throughput 99% of the time in a given year. Non-compliant periods are approximately uniformly distributed, targeting 99% of expected total throughput each hour. For more information, see Amazon EBS Volume Types.
When you enable EBS optimization for an instance that is not EBS–optimized by default, you pay an additional low, hourly fee for the dedicated capacity. For pricing information, see EBS-optimized Instances on the Amazon EC2 Pricing page.