How do Amazon EFS burst credits work?
Last updated: 2020-05-06
My Amazon Elastic File System (Amazon EFS) file system had great performance immediately after I created it, but now the performance is much lower. Does this have something to do with burst credits?
File-based workloads are typically spiky, driving high levels of throughput for short periods, but driving lower levels of throughput for longer periods. Amazon EFS is designed to burst to high throughput levels for periods of time.
There are two throughput modes for your file system: Bursting Throughput or Provisioned Throughput. With Bursting Throughput mode, throughput on Amazon EFS scales as your file system grows. With Provisioned Throughput mode, you can instantly provision the throughput of your file system independent of the amount of data stored. For more information, see Throughput modes.
All file systems have a permitted throughput, which is the maximum throughput you can drive the file system at any given point. This permitted throughput is either your baseline throughput or your burst throughput.
Both the baseline throughput and the burst throughput are based on the size of your file system. A metering process runs about every hour to determine the size of your file system. Based on the determined size, the process sets the baseline and burst throughput rates. When Amazon EFS lifecycle management is enabled, only the size of the data in Standard storage class is considered.
Amazon EFS uses a credit system that determines when file systems can burst. If the credit balance of your file system drops to zero, then your permitted throughput rate drops to your baseline throughput. When driving at baseline throughput, you use credits at the same rate you earn them.
When you have a positive burst credit balance, you can drive your file system at its burst throughput. However, when driving at burst throughput, you use credits faster than you can earn them. If this pace continues, you will use up all the credits, and your burst credit balance will drop to zero.
New file systems start out with 2.1 TiB of burst credits. This is why you can drive the new file system at burst throughput, despite having no data or metadata stored in the system. When the burst credits are used, then the performance of the new system is lowered.
For more information, see Throughput Scaling with Bursting mode.
With Provisioned Throughput, you can instantly provision the throughput of your file system and get the high levels of throughput that your applications require. This provisioning is independent of the amount of data stored. For more information, see Specifying Throughput with Provisioned mode.
Additional charges are associated with using Provisioned Throughput mode. Using Provisioned Throughput mode, you are billed for the storage that you use and throughput that you provision independently. For more information, see Amazon EFS pricing.
You can change between the Provisioned Throughput mode and the Bursting Throughput mode as long as more than 24 hours have elapsed since the last throughput mode change. You can increase the Provisioned Throughput values as many times as you want, but you can decrease the Provisioned Throughput value only once every 24 hours.
If the metered size of your file system provides a higher baseline rate than the throughput you provisioned, then your file system defaults to the Bursting Throughput model.