Monitor I/O characteristics using CloudWatch; Related resources; IOPS. IOPS are a unit of measure representing input/output operations per second. The operations are measured in KiB, and the underlying drive technology determines the maximum amount of data that a volume type counts as a single I/O. I/O size is capped at 256 KiB for SSD volumes …
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-io-characteristics.html