The answer is that the array was accidentally rebuilt as a RAID 1 mirror instead of RAID 10. In RAID 10, data is both mirrored and striped across all four drives, so with four 2 TB drives you get 4 TB of usable capacity—half the raw 8 TB total. If the controller rebuilds the array as a single RAID 1 mirror, it only uses two drives, yielding just 2 TB, which explains the capacity drop. On the CompTIA A+ Core 1 220-1201 exam, this question tests your understanding of RAID level capacity calculations and the common trap of misconfiguration after a drive replacement. A frequent mistake is assuming any healthy rebuild with identical drives will restore full capacity, but the controller’s configuration settings must explicitly specify RAID 10. To remember: RAID 10 is “mirror plus stripe,” so four drives give you two mirrored pairs striped together—if you lose the stripe, you lose half the space.
220-1201 Storage and RAID Troubleshooting Practice Question
This 220-1201 practice question tests your understanding of storage and raid troubleshooting. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 small business server with a RAID 10 array of four 2 TB hard drives experiences a drive failure. The technician replaces the failed drive with an identical model. After rebuilding, the array reports as healthy, but the total capacity is now 2 TB instead of the expected 4 TB. What is the most likely cause?
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 array was accidentally rebuilt as a RAID 1 mirror instead of RAID 10.
RAID 10 combines mirroring and striping. If the replacement drive is not properly sized or the array is misconfigured, capacity can be incorrect. However, the most common cause is using a drive with different geometry or the array being rebuilt as a single mirror instead of striped mirrors. This question tests understanding of RAID 10 capacity calculation.
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.
✗
The replacement drive has a different sector size.
Why it's wrong here
Different sector sizes can cause issues, but the capacity loss is more likely due to RAID configuration.
✓
The array was accidentally rebuilt as a RAID 1 mirror instead of RAID 10.
Why this is correct
Correct. If the controller treats the four drives as two mirrored pairs but only one pair is used, capacity would be 2 TB.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The new drive is 1 TB instead of 2 TB.
Why it's wrong here
If the drive were smaller, the array might not rebuild or would show reduced capacity, but 2 TB total suggests a different issue.
✗
The array is using a non-standard stripe size.
Why it's wrong here
Stripe size affects performance, not total capacity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
If the drive were smaller, the array might not rebuild or would show reduced capacity, but 2 TB total suggests a different issue.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 220-1201 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
Identify which 220-1201 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Storage and RAID Troubleshooting — This question tests Storage and RAID Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The array was accidentally rebuilt as a RAID 1 mirror instead of RAID 10. — RAID 10 combines mirroring and striping. If the replacement drive is not properly sized or the array is misconfigured, capacity can be incorrect. However, the most common cause is using a drive with different geometry or the array being rebuilt as a single mirror instead of striped mirrors. This question tests understanding of RAID 10 capacity calculation.
What should I do if I get this 220-1201 question wrong?
Identify which 220-1201 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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?
Read the scenario before looking for a memorised answer.
About these practice questions
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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 technician is tasked with setting up a RAID 10 array using four 500 GB HDDs for a database server. After configuration, the total capacity shown is 1 TB instead of the expected 1.5 TB. What is the most likely cause?
medium
A.One of the drives is only 250 GB.
B.The array was accidentally configured as RAID 0.
D.The controller is using a different stripe size.
Why C: RAID 10 (1+0) mirrors and then stripes, so usable capacity is half of total raw capacity (4 x 500 GB = 2 TB raw, 1 TB usable). The technician likely expected RAID 5 capacity (75% usable) but configured RAID 10.
Variation 2. A technician is configuring a RAID 10 array for a database server using four 500 GB SSDs. After setup, the array shows a total capacity of 1 TB instead of 2 TB. What is the most likely reason for this discrepancy?
medium
A.The RAID controller is faulty.
B.The array was accidentally configured as RAID 1.
C.The drives are not all the same size.
✓ D.RAID 10 uses half the total capacity for mirroring.
Why D: RAID 10 combines mirroring (RAID 1) and striping (RAID 0). With four drives, two mirrored pairs are created, so half the capacity is used for redundancy. The total usable capacity is (number of drives / 2) * drive size, which is 1 TB in this case.
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Question Discussion
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