This metric is not supported with Multi-Attach enabled volumes.
Used with Provisioned IOPS SSD volumes only. The percentage of I/O operations per second (IOPS) delivered of the total IOPS provisioned for an Amazon EBS volume.
Provisioned IOPS SSD volumes deliver their provisioned performance 99.9 percent of the time.
During a write, if there are no other pending I/O requests in a minute, the metric value will be 100 percent.
Also, a volume's I/O performance may become degraded temporarily due to an action you have taken (for example, creating a snapshot of a volume during peak usage, running the volume on a non-EBS-optimized instance, or accessing data on the volume for the first time).