AWS RDS Burst Balance

What Burst Balance Applies To

  • Burst balance only applies to General Purpose SSD storage (gp2). It does not apply to Magnetic storage, or Provisioned IOPS (io1).

Baseline Performance

  • Every SSD comes with a baseline performance, measured in IOPS (I/O (input/output) per second).

  • Each GB of storage provides 3 IOPS of baseline performance.

    • There is a minimum of 100 IOPS. So any SSD between 20-33 GB will have a baseline performance of 100 IOPS.

    • There is a maximum of 16,000 IOPS. So any SSD above 5340 GB will have a baseline performance of 16,000 IOPS.

    • Examples: 500 GB has 1,500 IOPS, 1,000 GB has 3,000 IOPS.

  • This baseline performance is guaranteed for your SSD. You will have this level of IOPS even if you have no burst balance remaining.

Burst

  • Bursting is having your SSD go over the baseline performance for a certain period of time.

  • The burst duration is dependent on the burst balance, which is related to how much it’s gone over the baseline, as well as the size of the SSD.

  • SSDs below 1,000 GB are able to burst to a maximum of 3,000 IOPS.

  • SSDs that are 1,000 GB and above do not have a maximum IOPS that they can burst to.

    • For this, the documentation says that burst is not relevant for SSDs above 1,000 GB. The phrase “not relevant” can be a little vague. Does it mean there’s no burst at all? Or does it mean it can burst to any value? From personal experience, the highest IOPS value I have seen my 1,000 GB SSD burst to is 15,000 IOPS).

Burst Balance

  • When the IOPS usage of your SSD goes above the baseline, burst balance is used.

  • When the IOPS usage goes below the baseline, burst balance is regenerated.

  • If your burst balance reaches 0%, your SSD will not perform any higher than the baseline IOPS. This can cause severe issues with your application performance if it relies too much on burst.

  • I feel that the actual calculations for this aren’t that important to know, because I don’t think you should be planning too much around using the burst balance due to the dangers of hitting 0%. Burst balance should be treated as a safety net, not something to be used regularly

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