DBS-C01 Deployment and Migration Practice Question
A company is migrating a 4 TB Oracle database to Amazon Aurora PostgreSQL using AWS DMS. The migration completes successfully but the application experiences high latency on the Aurora cluster. The DMS task used LOB mode 'full LOB mode'. What is the most likely cause of the latency?
⚠ Common exam trap
Many exam-takers assume 'full LOB mode' is always safe or that latency must be due to ongoing replication or network issues, but the real cause is the I/O impact of storing large LOBs in Aurora's storage engine.
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
✓
Full LOB mode caused large LOBs to be stored in the Aurora cluster, leading to increased I/O
Full LOB mode in AWS DMS loads entire LOBs into memory before writing them to the target, which can cause large LOBs to be stored in the Aurora cluster. This increases I/O and storage overhead, leading to high latency on the Aurora cluster, especially if the LOBs are significantly larger than the default chunk size or if the cluster's I/O capacity is exceeded.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The Aurora cluster was underprovisioned for parallel load
Why it's wrong here
Parallel load improves performance, not causes latency.
- ✓
Full LOB mode caused large LOBs to be stored in the Aurora cluster, leading to increased I/O
Why this is correct
Full LOB mode stores LOBs inline, which can cause write amplification and high latency.
- ✗
The DMS task was configured with 'ongoing replication' causing continuous write load
Why it's wrong here
Ongoing replication is normal and does not inherently cause high latency.
- ✗
The DMS task replicated data to a different region, causing network latency
Why it's wrong here
There is no mention of cross-region replication.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-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 DBS-C01 exam.