PAS-C01 Operations and Maintenance Practice Question
A company runs its SAP HANA database on an EC2 instance with multiple EBS volumes striped using LVM. The operations team notices increased latency and wants to ensure consistent I/O performance. What is the MOST effective way to monitor the average queue length of the EBS volumes?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Monitor the `VolumeQueueLength` CloudWatch metric for each EBS volume.
CloudWatch provides the `VolumeQueueLength` metric for EBS volumes, which is the best indicator of I/O queue depth.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Monitor the `VolumeQueueLength` CloudWatch metric for each EBS volume.
Why this is correct
This metric directly reports the number of pending I/O requests, which is the queue length.
- ✗
Enable detailed monitoring on the EC2 instance to get per-minute metrics.
Why it's wrong here
Detailed monitoring provides more frequent CPU/memory metrics, but does not include EBS queue length.
- ✗
Create a custom CloudWatch metric using the `QueueDepth` performance counter from the OS.
Why it's wrong here
This is possible but unnecessary as the metric is already available.
- ✗
Use the `iostat` command on the EC2 instance to monitor device queue length.
Why it's wrong here
`iostat` reports queue length from the operating system’s block-device layer, which reflects the LVM logical volume’s queue, not the individual EBS volume queues. The correct approach must use CloudWatch metrics (`VolumeQueueLength`) to capture the actual EBS device-level queue length that AWS measures. This option is tempting because `iostat` is a standard Linux tool for monitoring disk I/O performance and would be correct if the goal were to observe the OS-level queue on a non-striped, single-volume setup.
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