Question 815 of 972
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220-1201 Practice Question: A customer reports that their computer with a…
A customer reports that their computer with a RAID 5 array is running very slowly during file transfers. The system uses three 1 TB SATA hard drives. The technician runs a diagnostic and finds that one drive has a high number of reallocated sectors. What is the most likely cause of the performance issue?
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
✓
One of the drives is failing and the array is operating in degraded mode.
In a RAID 5 array, if one drive is failing (e.g., high reallocated sectors), the array may still be operational but performance degrades significantly because the controller must reconstruct data on the fly from parity information. This scenario tests understanding of RAID 5 behavior during drive degradation.
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 RAID controller is overheating.
Why it's wrong here
An overheating RAID controller can indeed cause system instability, intermittent errors, or overall performance degradation. However, the diagnostic finding of "high reallocated sectors" specifically points to a physical problem with a storage drive itself, indicating bad sectors. A controller thermal issue would typically manifest with different error codes, system crashes, or fan warnings, rather than drive-specific sector reallocation counts.
- ✓
One of the drives is failing and the array is operating in degraded mode.
Why this is correct
High reallocated sectors are a critical indicator of a failing hard disk drive, signifying that the drive's firmware is attempting to remap unreadable sectors. When a drive in a RAID array, especially RAID 5 or 6, experiences such failure, the array enters a degraded state. In this mode, the RAID controller must reconstruct missing data using parity from the remaining drives, which significantly increases I/O operations and causes a noticeable performance slowdown.
- ✗
The array is configured with the wrong stripe size.
Why it's wrong here
Stripe size, or block size, is a fundamental configuration parameter established when a RAID array is initially created. While an improperly chosen stripe size can lead to suboptimal performance from the outset, it would not cause a sudden, progressive slowdown correlated with drive errors. Furthermore, a stripe size misconfiguration would not result in diagnostic reports of "high reallocated sectors," which are indicative of a developing hardware fault within a drive.
- ✗
The operating system is defragmenting the array.
Why it's wrong here
Defragmentation is a software process that reorganizes fragmented data on a drive to improve file access efficiency, and it can temporarily increase disk activity and reduce performance. However, this operation does not cause physical drive errors like "high reallocated sectors." These sector reallocations are a direct symptom of a failing drive's hardware, indicating a much more serious underlying issue than mere data fragmentation.
Quick reference
RAID Level Comparison
| RAID Level | Min Disks | Fault Tolerance | Read | Write | Usable Capacity |
|---|---|---|---|---|---|
| RAID 0 | 2 | None | Excellent | Excellent | 100% |
| RAID 1 | 2 | 1 disk | Good | Moderate | 50% |
| RAID 5 | 3 | 1 disk | Good | Moderate | 67–94% |
| RAID 6 | 4 | 2 disks | Good | Lower | 50–88% |
| RAID 10 | 4 | 1 disk per mirror | Excellent | Good | 50% |
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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Last reviewed: Jun 18, 2026
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