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220-1201 Practice Question: During a hardware installation, you are tasked…
During a hardware installation, you are tasked with setting up a RAID 1 array in a server using two identical 4 TB HDDs. After configuration, the total usable capacity is only 4 TB. Is this expected behavior?
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
✓
Yes, RAID 1 provides fault tolerance by mirroring data, so usable capacity is 4 TB.
RAID 1 mirrors data across two drives, so usable capacity equals the size of one drive (4 TB). This provides redundancy, not increased storage. RAID 0 would combine capacity, and RAID 5 requires at least three drives.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
No, the array should show 8 TB because the drives are identical.
Why it's wrong here
RAID 1, also known as mirroring, creates an exact duplicate of data on both drives. Therefore, even with two identical 4 TB drives, the usable storage capacity remains 4 TB because the second drive is dedicated entirely to redundancy, not increasing total space. The identical nature of the drives ensures consistent mirroring but does not combine their capacities to 8 TB.
- ✓
Yes, RAID 1 provides fault tolerance by mirroring data, so usable capacity is 4 TB.
Why this is correct
This statement is correct because RAID 1's fundamental purpose is to provide fault tolerance by maintaining an identical copy of data across two or more drives. With two 4 TB drives configured in RAID 1, one drive mirrors the other, resulting in a total usable capacity equivalent to a single drive, which is 4 TB. This configuration ensures data availability even if one drive fails.
- ✗
No, the array should be configured as RAID 0 to get 8 TB.
Why it's wrong here
While configuring the drives as RAID 0 (striping) would indeed combine the capacities of two 4 TB drives to achieve 8 TB, this configuration offers no data redundancy or fault tolerance. RAID 0 distributes data across both drives without duplication, meaning the failure of a single drive results in the complete loss of all data in the array. This contradicts the implied need for data protection often associated with server installations.
- ✗
Yes, but only if the drives are set as JBOD.
Why it's wrong here
JBOD, or Just a Bunch of Disks, concatenates multiple drives into a single logical volume, effectively combining their capacities without any form of redundancy or mirroring. While two 4 TB drives in a JBOD configuration would present as an 8 TB volume, this setup does not provide fault tolerance. Unlike RAID 1, JBOD offers no protection against drive failure, as data is simply written sequentially across the disks.
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
Laptop Hardware and Components
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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