The correct answer is the FreeStorageSpace metric with an alarm threshold set to less than 10% of the allocated storage, such as 10 GB on a 100 GB RDS instance. This is because FreeStorageSpace measures the actual available bytes remaining on the DB instance’s allocated storage, making it the precise metric to trigger an alert when free space drops below a specific absolute value. On the AWS Certified Database Specialty DBS-C01 exam, this question tests your understanding that CloudWatch monitors raw storage in bytes, not percentages, so you must calculate the threshold manually based on allocated size. A common trap is choosing a percentage-based condition like “less than 10% of total,” which CloudWatch does not natively support for FreeStorageSpace, or confusing it with BinaryLog usage. Memory tip: think “FreeStorageSpace = free bytes, so set a fixed byte threshold equal to 10% of your allocated GB.”
DBS-C01 Monitoring and Troubleshooting Practice Question
This DBS-C01 practice question tests your understanding of monitoring and troubleshooting. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 company runs an Amazon RDS for Oracle DB instance. The database administrator wants to receive an alert when the storage space is below 10% of the allocated storage. Which Amazon CloudWatch metric and alarm threshold should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Metric: FreeStorageSpace, Condition: < 10% of 100 GB (10 GB)
The metric FreeStorageSpace shows the available storage in bytes. The alarm should be set to when FreeStorageSpace is less than 10% of allocated storage. Option B is correct. Option A is wrong because it's a percentage of total. Option C is wrong because it's a fixed value. Option D is wrong because BinaryLog usage is not relevant.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Metric: FreeStorageSpace, Condition: < 10% of 100 GB (10 GB)
Why this is correct
FreeStorageSpace metric with a threshold of 10 GB (assuming 100 GB allocated) would trigger when free space is below 10%.
Related concept
Standard ACLs match source addresses.
✗
Metric: BinaryLogUsage, Condition: > 10%
Why it's wrong here
BinaryLogUsage is for MySQL binlog, not Oracle.
✗
Metric: FreeableMemory, Condition: < 10% of total memory
Why it's wrong here
FreeableMemory is for RAM, not storage.
✗
Metric: DiskQueueDepth, Condition: > 10
Why it's wrong here
DiskQueueDepth indicates I/O wait, not storage space.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DBS-C01 ACL questions on filtering logic and placement.
Monitoring and Troubleshooting — This question tests Monitoring and Troubleshooting — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Metric: FreeStorageSpace, Condition: < 10% of 100 GB (10 GB) — The metric FreeStorageSpace shows the available storage in bytes. The alarm should be set to when FreeStorageSpace is less than 10% of allocated storage. Option B is correct. Option A is wrong because it's a percentage of total. Option C is wrong because it's a fixed value. Option D is wrong because BinaryLog usage is not relevant.
What should I do if I get this DBS-C01 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DBS-C01 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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