PAS-C01 Operations and Maintenance Practice Question
A company runs a multi-tier application on AWS. The application consists of an Application Load Balancer (ALB) that distributes traffic to a fleet of EC2 instances running a web server. The web servers write logs to an Amazon EFS file system mounted across all instances. The operations team reports that the web application is experiencing intermittent high latency and timeouts. Monitoring shows that the ALB's target response time is normal, but the application's internal processing time is high. Further investigation reveals that the EFS performance metrics show high 'BurstCreditBalance' and 'PercentIOLimit' during the latency spikes. The EFS file system is configured with 'Bursting' throughput mode. The team needs to resolve the latency issue with minimal cost. What should they do?
⚠ Common exam trap
Test-takers frequently assume 'Bursting' mode is always sufficient and look to add compute capacity (Option C) or change storage type (Option A), when the real issue is that the file system is too small to sustain the workload's I/O demands, and resizing it is the most cost-effective fix.
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
✓
Increase the size of the EFS file system to increase the baseline throughput and burst credits.
Increasing the size of an EFS file system in Bursting mode raises its baseline throughput and burst credit accumulation rate. The high BurstCreditBalance and PercentIOLimit indicate the file system is exhausting its burst credits and hitting its I/O limit, causing throttling and latency. A larger EFS volume provides a higher baseline throughput, reducing reliance on burst credits and smoothing performance without additional cost for Provisioned Throughput.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Migrate the log files to Amazon S3 and use S3 Transfer Acceleration for writes.
Why it's wrong here
S3 is not a POSIX-compliant file system; rewriting applications to use S3 is costly and complex.
- ✗
Switch the EFS throughput mode to Provisioned Throughput to guarantee higher performance.
Why it's wrong here
Provisioned Throughput incurs higher cost; increasing file system size is more cost-effective if baseline throughput suffices.
- ✗
Add more EC2 instances to the Auto Scaling group to distribute the I/O load.
Why it's wrong here
More instances increase concurrent I/O, potentially worsening the bottleneck.
- ✓
Increase the size of the EFS file system to increase the baseline throughput and burst credits.
Why this is correct
Larger EFS file systems have higher baseline throughput and accumulate more burst credits, reducing I/O wait.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PAS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PAS-C01 exam.