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220-1201 Practice Question: A technician is troubleshooting a server that…

A technician is troubleshooting a server that uses a RAID 5 array with three 1TB HDDs. One drive fails, and the technician replaces it with a new 1TB HDD. After rebuilding, the array reports only 1.8TB of usable space. What is the most likely cause?

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

The replacement drive has a slightly smaller actual capacity than the original drives.

This question tests advanced RAID understanding. RAID 5 uses one drive's worth of capacity for parity, so three 1TB drives yield 2TB usable. The loss of 0.2TB suggests the replacement drive has slightly less capacity due to manufacturer differences or sector mapping.

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 new drive has a different sector size (4K vs 512e).

    Why it's wrong here

    A different sector size (e.g., 4K native vs. 512-byte emulation or vice-versa) primarily affects how data is physically read and written on the drive, impacting performance and compatibility with the RAID controller or operating system. While a significant mismatch might prevent the drive from being recognized or integrated into the array at all, it does not inherently reduce the drive's total raw storage capacity. The reported 0.2TB capacity loss indicates a fundamental difference in the total number of available bytes, not an issue related to sector addressing.

  • The RAID controller is using some space for metadata.

    Why it's wrong here

    RAID controllers do utilize a small portion of each drive for storing metadata, which includes critical configuration information such as the array's structure, stripe size, and drive order. This metadata is essential for the controller to properly manage and rebuild the array. However, the space consumed by RAID metadata is typically negligible, usually amounting to only a few megabytes or, at most, a few gigabytes per drive. It would not account for a substantial 200GB (0.2TB) reduction in the array's total usable capacity.

  • The replacement drive has a slightly smaller actual capacity than the original drives.

    Why this is correct

    Hard drive manufacturers commonly advertise capacity using decimal (base-10) prefixes, where 1 TB equals 1,000,000,000,000 bytes. However, operating systems and RAID controllers often calculate and report capacity using binary (base-2) prefixes, where 1 TiB equals 1,099,511,627,776 bytes. This discrepancy can lead to a perceived capacity difference. More critically, in a RAID array, the total usable capacity is determined by the smallest drive member. If the replacement drive has a slightly lower actual byte count than the original drives, the entire array's capacity will be truncated to match the smallest drive, resulting in the observed 0.2TB loss.

  • The RAID 5 array is degraded and needs a second drive to be replaced.

    Why it's wrong here

    A degraded RAID 5 array signifies that one of the member drives has failed, and the array is operating in a fault-tolerant state using the remaining drives and parity information. While the array's redundancy is compromised, the total logical capacity presented to the operating system remains unchanged. The array continues to function and provide access to all data at its full original capacity. Replacing a failed drive restores redundancy but does not alter the overall storage capacity of the array itself.

Quick reference

RAID Level Comparison

RAID LevelMin DisksFault ToleranceReadWriteUsable Capacity
RAID 02NoneExcellentExcellent100%
RAID 121 diskGoodModerate50%
RAID 531 diskGoodModerate67–94%
RAID 642 disksGoodLower50–88%
RAID 1041 disk per mirrorExcellentGood50%

RAID is not a backup strategy — it protects against disk failure but not against accidental deletion, ransomware, or site-level events.

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JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This 220-1201 practice question is part of Courseiva's free CompTIA 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 220-1201 exam.