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220-1201 Practice Question: A technician is configuring a RAID 10 array for a…
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?
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
✓
RAID 10 uses half the total capacity for mirroring.
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.
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 faulty.
Why it's wrong here
A faulty RAID controller would typically manifest as an inability to detect drives, an array failing to initialize, persistent I/O errors, or complete system instability. It is highly unlikely for a faulty controller to perfectly configure an array that operates stably but consistently reports a specific, reduced capacity that aligns with the expected behavior of a particular RAID level. The scenario describes a functional array with a predictable capacity, which points away from a hardware malfunction.
- ✗
The array was accidentally configured as RAID 1.
Why it's wrong here
Configuring a four-drive array as RAID 1 (mirroring) would result in a usable capacity equivalent to a single drive. With four 500 GB drives, RAID 1 would mirror the data across all drives, providing only 500 GB of usable storage, not the 1 TB observed in the scenario. RAID 1 prioritizes data redundancy by duplicating all data, effectively making the total capacity equal to the smallest drive in the mirror.
- ✗
The drives are not all the same size.
Why it's wrong here
The question explicitly states that the technician is configuring a RAID 10 array for four 500 GB drives. Therefore, the premise of this option, that the drives are not all the same size, directly contradicts the given information. If drives of different sizes were used in a RAID array, the controller would typically default to the capacity of the smallest drive for all members, or the array might fail to build entirely.
- ✓
RAID 10 uses half the total capacity for mirroring.
Why this is correct
RAID 10, also known as RAID 1+0, combines mirroring (RAID 1) and striping (RAID 0). It first creates mirrored pairs of drives, and then stripes data across these mirrored sets. With four 500 GB drives, two 500 GB drives form a 500 GB mirrored volume, and the other two form a second 500 GB mirrored volume. These two 500 GB logical volumes are then striped together, resulting in a total usable capacity of 1 TB, which is exactly half of the raw 2 TB capacity.
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.
Go deeper
Related to this question
Learn chapter
Troubleshoot: Storage and RAID
Key term
RAID 0
RAID 0 is a storage configuration that combines multiple hard drives into one logical unit to improve speed and capacity, but with no fault tolerance or data protection.
Key term
Redundant Array of Independent Disks
A technology that combines multiple physical hard drives into a single logical unit to improve performance, reliability, or both.
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Written by Johnson Ajibi, MSc IT Security
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