The answer is the target RDS instance throttling write operations due to low IOPS. When AWS DMS migration slows because of target write throttling, the replication instance’s CPU remains low—often below 10%—because it is not the bottleneck; instead, the target database cannot keep up with the incoming writes, creating an IOPS bottleneck that forces DMS to wait. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding that DMS performance issues are frequently caused by the target’s limited write capacity, not by the replication instance or source. A common trap is to blame the DMS instance or task configuration, but the key clue is low CPU utilization on the replication instance paired with slow progress. Remember the memory tip: “Low CPU on DMS means the target is the boss”—if the replication instance is idle, look downstream at the target’s IOPS limits.
DBS-C01 Management and Operations Practice Question
This DBS-C01 practice question tests your understanding of management and operations. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A database administrator is using AWS DMS to migrate an on-premises Oracle database to Amazon RDS for PostgreSQL. The migration has been running for several hours, but the full load phase is taking much longer than expected. The CPU utilization on the DMS replication instance is consistently below 10%. What is the MOST likely cause of the slow performance?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The target RDS instance is throttling write operations due to low IOPS.
Option C is correct because when migrating to a target with limited write capacity (e.g., RDS instance with low IOPS), DMS may be throttled by the target's write throughput, while the replication instance itself is underutilized. Option A is incorrect because DMS can use multiple tasks, but the issue is not about parallelism. Option B is incorrect because DMS uses its own engine, not PostgreSQL. Option D is incorrect because using LOBs can slow down migration, but the symptom is low CPU on the replication instance, not high.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 source database has large LOBs that are being transferred in full LOB mode.
Why it's wrong here
Large LOBs can slow migration but would cause higher CPU usage.
✗
The target database engine is not compatible with DMS.
Why it's wrong here
DMS supports Oracle to PostgreSQL migration.
✗
The DMS task is not configured to use parallel tables.
Why it's wrong here
Parallel load could help, but the symptom suggests target throttling.
✓
The target RDS instance is throttling write operations due to low IOPS.
Why this is correct
Low IOPS on the target can cause DMS to wait, leading to low CPU on the replication instance.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
Management and Operations — This question tests Management and Operations — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The target RDS instance is throttling write operations due to low IOPS. — Option C is correct because when migrating to a target with limited write capacity (e.g., RDS instance with low IOPS), DMS may be throttled by the target's write throughput, while the replication instance itself is underutilized. Option A is incorrect because DMS can use multiple tasks, but the issue is not about parallelism. Option B is incorrect because DMS uses its own engine, not PostgreSQL. Option D is incorrect because using LOBs can slow down migration, but the symptom is low CPU on the replication instance, not high.
What should I do if I get this DBS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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