One of the common performance issues in EC2 is related to Elastic Block Storage (EBS), which is a storage service offered by AWS. EBS volumes can experience unpredictable disk I/O, leading to performance degradation. This issue arises due to two main reasons:
- Standard EBS volumes are slow: Standard EBS volumes have limited IOPS (input/output operations per second) capacity, averaging around 100 IOPS for blocks of 16KB or less. This can become a bottleneck when the I/O operations on the volume increase and reach the IOPS limit, causing I/O operations to queue up and resulting in increased latency and slower application performance.
- Shared hardware for EBS: The underlying storage devices and storage network for EBS are shared among multiple customers. This shared infrastructure can introduce variability in latency and IOPS performance. The behavior of other users sharing the same storage system can impact the latency experienced by your application.
To detect this issue, you can monitor the VolumeQueueLength metric provided by AWS CloudWatch. A sustained increase in the VolumeQueueLength metric above one on a standard EBS volume indicates that the throughput of the volume is being exhausted. Additionally, if the sustained increase in VolumeQueueLength is way above the number of provisioned IOPS divided by 100, it also indicates throughput exhaustion.
Here are some strategies to address the unpredictable EBS disk I/O issue:
- Select the right storage and instance types: Understand the I/O needs of your application and choose the appropriate EBS storage types. Consider using RAID to pool together EBS volumes, opting for Provisioned IOPS volumes, or exploring solid-state drives (SSD) as alternatives to standard EBS volumes.
- Prime your EBS volumes: Accessing all blocks on an EBS volume at least once can help improve performance. You can run a command to read all blocks on the EBS volume once to prime it for optimal performance.
- Consider Instance Store: Instance Store provides dedicated storage on the EC2 server and can offer more predictable I/O performance compared to EBS. However, it comes with limitations and management considerations, such as the lack of data persistence if the server fails.
- Purchase Provisioned IOPS: If guaranteed IOPS availability is crucial for your application, you can purchase Provisioned IOPS volumes from AWS. However, be aware that these packages come at a higher cost.
- Replace degraded EBS volumes: If you have configured your EBS volumes using RAID, you can decommission and replace a problematic volume without disruption. Alternatively, if you have frequent snapshots, you can copy data from a snapshot to replace the degraded volume, although this process may impact bandwidth and storage latency.
- Wait for EBS latency to drop: If the performance issue is caused by external factors such as other customers' workloads or network traffic, waiting for the situation to normalize may improve performance.
It's important to note that the performance characteristics of EBS volumes can vary over time, so ongoing monitoring and adjustments may be necessary to maintain optimal performance for your EC2 instances.
