Part 5: Understanding Amazon Elastic Block Store Performance: Latency

Understanding the latencies

In general, it is impossible for a storage system to sustain the same peak IOPS number when presented with different I/O types and latency requirements.  Only IOPS numbers alone are meaningless without considering additional metrics such as latency, read/write % and I/O block size etc.

Latency is a measure of how long it takes for a single I/O request to happen from the apps perspective. High Latency and variance is not preferred when it comes to database applications. Database makes variety of requests and ideally IO latency needs to be under 10ms and write especially under 5ms. Example: In Oracle DB with for heavy writes, the redo log under 1ms is preferred. On the other hand, applications doing sequential, throughput-driven I/O (like backup or archival) typically don’t need high IOPS, but rather need high MB/s.

PIOPS Volumes delivers consistent level of latency and performance than standard EBS Volumes on random reads and random read/writes.  In the benchmark conducted by parse, PIOPS showed latency between 0-0.6 seconds and Standard EBS volumes showed 0.0 to 2.5 seconds. Refer URL:

http://blog.parse.com/2012/09/17/parse-databases-upgraded-to-amazon-provisioned-iops/

On the other hand, for random writes you should expect to see roughly similar latencies between Standard and Provisioned IOPS volumes, whereas on sequential writes and reads you can observe Standard EBS performing better than PIOPS sometimes. 


EBS Article Series (continued..)

Part 1: Understanding Amazon Elastic Block Store
Part 2: Understanding Standard EBS Volumes
Part 3: Understanding EBS PIOPS Volumes
Part 4: Understanding EBS-Optimized Instances
Part 5: Understanding Latency in EBS
Part 7: 10% of your provisioned IOPS 99.9% of the time
Part 8: Performance Tuning - Pre Warming the EBS volume
Part 9: Performance Tuning - EBS Striping
Part 10: Performance Tuning - IO Block Size
Part 11: Understanding Amazon EBS Snapshots
Part 12: Securing Amazon EBS volumes - EBS Encryption using SecureCloud 
Part 13: Amazon EBS Security Best practices and tips