The answer is synchronous replication over dedicated low-latency fiber links. This strategy meets the 1-minute RPO and 15-minute RTO because it writes data to both the primary and secondary sites simultaneously before acknowledging the write to the application, ensuring zero data loss at the storage layer. Over a 50-mile distance, dedicated fiber keeps round-trip time under 1 millisecond, allowing rapid failover within the 15-minute window while guaranteeing transactional consistency. On the CompTIA SecurityX CAS-004 exam, this scenario tests your understanding of RPO/RTO trade-offs and the physical limitations of distance; a common trap is choosing asynchronous replication, which introduces lag and fails the 1-minute RPO. Remember the key distinction: synchronous equals zero data loss but requires low latency, while asynchronous sacrifices RPO for distance tolerance. Memory tip: “Sync for zero, async for far.”
CAS-004 Security Architecture Practice Question
This CAS-004 practice question tests your understanding of security architecture. 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 large enterprise is designing a disaster recovery site that must support rapid failover with minimal data loss. The primary data center is 50 miles away. The RPO is 1 minute, and RTO is 15 minutes. Which replication strategy best meets these requirements?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Synchronous replication over dedicated low-latency fiber links.
Synchronous replication writes data to both the primary and secondary sites simultaneously before acknowledging the write to the application, ensuring zero data loss at the storage layer. With dedicated low-latency fiber links over 50 miles, the round-trip time can be kept under 1 ms, meeting the 1-minute RPO and enabling rapid failover within the 15-minute RTO. This strategy guarantees transactional consistency and immediate availability at the DR site.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Log shipping with a 5-minute delay.
Why it's wrong here
Log shipping with delay exceeds the RPO.
✓
Synchronous replication over dedicated low-latency fiber links.
Why this is correct
Synchronous replication ensures zero data loss and can meet the required RPO and RTO if latency is low enough.
Clue confirmation
The clue words "best", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Scheduled snapshot-based replication every 30 minutes.
Why it's wrong here
Snapshots every 30 minutes do not meet the 1-minute RPO.
✗
Asynchronous replication with continuous data protection.
Why it's wrong here
Asynchronous replication may have seconds to minutes of lag, potentially exceeding the 1-minute RPO.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose asynchronous replication (Option D) thinking 'continuous data protection' implies zero data loss, but they overlook that asynchronous replication inherently introduces a write acknowledgment delay, which can still result in data loss during a failure, and the recovery process may not meet the aggressive RTO.
Detailed technical explanation
How to think about this question
Synchronous replication relies on the SCSI-3 persistent reservation and SPC-4 commands to maintain write ordering across sites, and the 50-mile distance requires fiber-optic links with sub-millisecond latency (typically ≤1 ms round-trip) to avoid application performance degradation. In practice, enterprises often use Fibre Channel over IP (FCIP) or dedicated DWDM wavelengths to achieve the necessary low latency, and the replication is typically implemented at the storage array level (e.g., Dell EMC SRDF/S or HPE Peer Persistence).
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the CAS-004 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Architecture — This question tests Security Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Synchronous replication over dedicated low-latency fiber links. — Synchronous replication writes data to both the primary and secondary sites simultaneously before acknowledging the write to the application, ensuring zero data loss at the storage layer. With dedicated low-latency fiber links over 50 miles, the round-trip time can be kept under 1 ms, meeting the 1-minute RPO and enabling rapid failover within the 15-minute RTO. This strategy guarantees transactional consistency and immediate availability at the DR site.
What should I do if I get this CAS-004 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best", "primary". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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