Why does AWS RDS still shows burst balance 0 with disk size 2TB gp2?

Question

According to what I know about gp2 from AWS docs (link), gp2 disks have burst capabilily when they are smaller than 1000GB. After disk is bigger 1000GB, baseline performance exceeeds 3000 IOPS burst performance, so that "burst" term cannot apply.

However, as I see on my current prod database with 2TB gp2 storage, burst balance still somehow apply to me, and storage is considerably faster while burst balance is more than 0.

Apparently, there are changes in AWS Burst term. Does anybody knows modern terms, so I can plan my hardware accordingly?

Answer 1

I made request to AWS support about this. It was a lengthy thread where I got to know several important facts. I have saved my conversation at this link, so it's not lost for community.

Answer: burts balance may still apply for storage bigger than 1TB, because there may be several volumes to serve storage space. If volume is smaller than 1TB - burst balance gets utilized for that volume.

Other facts that were obscure for me:

• database may look like it's capped by IOPS limits (due internal IOPS submerge operation), but in reality it may be capped by network throughput.
• network throughput is gueranteed by EBS-Optimized. At RDS docs you won't find explicit tables how instances relate to throughput, but it's there on EBS docs
• For some of the instances that are nitro-based, EBS-Optimized allows to work at maximum throughput for class for 30 minutes each 24 hours. For smaller instances it means that for 30 minutes database may go skyrocket performance, comprared to poor baseline.

Answer 2

I've run into that issue with EFS, provisioning enough capacity (storage and throughput) is one thing, provisioning burst capacity is something else. In this case it appears that you are running into the same issue. Exceeding your burst capacity. If you have a read-heavy application, consider using a replica or a caching scheme. Alternatively you can increase your 2TB disk to 4TB or look into provisioned iops solution.