Find whether volume throughput, volume IOPS or the instance EBS-optimised limit caps your storage performance.
Storage performance is the minimum of three independent ceilings: what the volumes can deliver in MB/s, what their IOPS budget delivers once you multiply by the average block size, and what the instance's EBS-optimised channel allows in total. Block size is the hinge — at 4 KB the IOPS limit binds long before throughput, while at 256 KB or more the throughput limit binds first. Adding volumes or provisioning more IOPS does nothing once the instance EBS-optimised limit is the binding constraint, so identifying which of the three ceilings is active tells you whether to change the volume or the instance.
EC2 EBS Bandwidth
achievable MB/s = min(volumes × volume MB/s, volumes × volume IOPS × block size, instance EBS bandwidth).
achievable MB/s = min(volumes × volume MB/s, volumes × volume IOPS × block size, instance EBS bandwidth). Storage performance is the minimum of three independent ceilings: what the volumes can deliver in MB/s, what their IOPS budget delivers once you multiply by the average block size, and what the instance's EBS-optimised channel allows in total. Block size is the hinge — at 4 KB the IOPS limit binds long before throughput, while at 256 KB or more the throughput limit binds first.
Adding volumes or provisioning more IOPS does nothing once the instance EBS-optimised limit is the binding constraint, so identifying which of the three ceilings is active tells you whether to change the volume or the instance.
This calculator takes 6 inputs: Instance EBS bandwidth limit, Instance EBS IOPS limit, Volumes attached, Throughput provisioned per volume, IOPS provisioned per volume, Average I/O block size. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Because the IOPS budget caps you first. Four gp3 volumes at 3000 IOPS give 12,000 IOPS, which at 16 KB is only about 188 MB/s regardless of the 250 MB/s each volume is rated for. Larger I/O sizes, or more provisioned IOPS, are the only ways up.