Troubleshooting RDS gp2 Storage Performance — Burst Balance, Disk Queue, Low Space
A database administrator is monitoring an Amazon RDS for MySQL instance and sees the following CloudWatch metrics: 'DiskQueueDepth' is consistently at 10, 'WriteLatency' is 20 ms, 'FreeStorageSpace' is less than 10% of total. The instance uses gp2 storage. Which THREE actions should be taken to improve performance?
Quick Answer
The answer is to delete unnecessary data, increase storage, and switch to Provisioned IOPS. These three actions directly address the root causes of gp2 I/O performance degradation: low free storage space throttles baseline IOPS because gp2 relies on a 3 IOPS per GB ratio, while a consistently high DiskQueueDepth of 10 with 20 ms WriteLatency signals a saturated I/O channel that Provisioned IOPS can resolve by guaranteeing consistent throughput. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding that gp2’s burst balance is tied to storage size and that freeing space or increasing volume size restores baseline performance—a common trap is confusing Multi-AZ as a performance fix when it actually adds synchronous replication overhead. Remember the mnemonic: “Free, Big, Provisioned” — free space, bigger storage, and provisioned IOPS are the three levers for gp2 I/O bottlenecks.
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
✓
Switch to Provisioned IOPS (io1 or io2) for consistent performance
High 'WriteLatency' and 'DiskQueueDepth' indicate an I/O bottleneck. Switching to Provisioned IOPS (io1 or io2) provides consistent low-latency I/O performance. Option B is correct: gp2 storage baseline IOPS scales with storage size. Increasing allocated storage raises the baseline IOPS, which can improve performance. Option C is correct: Low free storage space on gp2 can cause performance degradation because write operations may be throttled. Deleting unnecessary data frees up space and alleviates this issue. Option D is incorrect: Multi-AZ provides high availability and disaster recovery, not increased I/O capacity. It can add write latency due to synchronous replication. Option E is incorrect: Performance Insights is a monitoring tool for analyzing database performance; it helps identify slow queries but does not directly improve performance. Therefore, the correct actions are A, B, and C.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Switch to Provisioned IOPS (io1 or io2) for consistent performance
Why this is correct
Provisioned IOPS ensures consistent I/O performance regardless of storage size.
- ✓
Increase allocated storage to improve baseline IOPS
Why this is correct
gp2 baseline IOPS scales with storage size; more storage means more IOPS.
- ✓
Delete unnecessary data to free up storage space
Why this is correct
Freeing storage space can improve performance because gp2 performance degrades when storage is nearly full.
- ✗
Enable Multi-AZ to increase I/O capacity
Why it's wrong here
Multi-AZ is for high availability, not I/O performance.
- ✗
Enable Performance Insights to identify slow queries
Why it's wrong here
Performance Insights helps identify issues but does not directly improve performance.
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Same concept, more angles
1 more way this is tested on DBS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A database administrator is troubleshooting an Amazon RDS for SQL Server instance that is experiencing high 'ReadIOPS' and 'ReadLatency'. The instance uses General Purpose SSD (gp2) storage. The 'BurstBalance' metric is 0%. What should the administrator do to improve performance?
medium- A.Enable Multi-AZ to distribute the load
- ✓ B.Increase the allocated storage or switch to Provisioned IOPS
- C.Create a read replica to offload read traffic
- D.Disable automatic backups to reduce I/O
Why B: When BurstBalance is 0%, the gp2 volume has exhausted its burst credits and is operating at baseline IOPS. To improve performance, you can increase the volume size (which increases baseline IOPS) or switch to Provisioned IOPS (io1/io2) for consistent performance. Option A is wrong because enabling Multi-AZ does not increase I/O performance; it provides high availability. Option C is wrong because creating a read replica offloads read traffic but does not improve write performance or reduce latency on the primary instance. Option D is wrong because disabling automatic backups reduces storage I/O but does not directly improve ReadIOPS or ReadLatency; the primary issue is exhausted burst credits.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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