RAID 10 vs RAID 5 Capacity Downside
Short answer
A RAID 10 mirrors every drive pair before striping, consuming half the raw storage and leaving less usable capacity than the parity-based RAID 5.
Question
Key Takeaways
The question tests understanding of how each RAID level calculates usable capacity; the common trap is assuming RAID 10 is worse on speed or redundancy, when its real cost is storage efficiency.
This A+ 220-1201 question compares RAID 10 (mirrored sets striped together) with RAID 5 (striped with distributed parity) to identify the main trade-off of RAID 10. The page establishes that RAID 10 sacrifices usable capacity, since half of the raw drive space is consumed by mirrored copies.
Common mistake: Option C (slower write speeds) is the typical wrong pick, because learners associate RAID overhead with degraded writes — but RAID 5, not RAID 10, suffers parity-calculation write penalties, and RAID 10 writes are generally fast.
Expert Analysis
Why the Answer Is Correct
RAID 10 combines mirroring (RAID 1) with striping (RAID 0), so every bit is stored twice across paired drives; usable capacity is exactly 50% of raw storage (e.g., four 1 TB drives yield only 2 TB usable). RAID 5 uses distributed parity that consumes only one drive's worth of space, so the same four drives yield about 3 TB usable. That difference — throwing away half the raw capacity for mirroring — is precisely the downside of choosing RAID 10 over RAID 5.
Why the Other Options Are Wrong
Option B is incorrect because redundancy is not reduced: RAID 10 tolerates at least one drive failure per mirror pair (and often more), which is comparable to or better than RAID 5's single-drive-failure tolerance, especially during a rebuild. Option C is wrong because RAID 10 writes go straight to mirrored disks with no parity computation, while RAID 5 pays a substantial parity write penalty, so RAID 10 writes are typically faster. Option D is also wrong because RAID 10 reads are very fast, since data can be pulled from either side of each mirror in parallel.
Community Comment Notes
A learner identified the answer as "Less capacity 🧸 RAID 10 uses half its drives for mirrored copies, so you sacrifice more usable storage capacity." That reasoning aligns with the standard RAID capacity formulas and confirms the mirror-versus-parity trade-off as the deciding factor.
Official Reference
https://www.comptia.org/certifications/a
This link opens the official vendor documentation in a new tab.
Exam Strategy
On RAID questions, quickly compute usable capacity for each level: RAID 1/10 = 50% of raw, RAID 5 = (n−1)/n, RAID 6 = (n−2)/n. Then recall that parity-based levels (5 and 6) are the ones penalized on writes, which eliminates speed-related distractors.
Frequently Asked Questions
Why isn't slower write speed a downside of RAID 10 versus RAID 5?
How much usable capacity does RAID 10 give compared to RAID 5?
Discussion 2 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 2
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Afie 👍 1 Answered ARAID 10 (1+0) combines mirroring and striping, requiring 50% of total drive capacity to be used for duplication. Example: Four 1TB drives = 2TB usable. RAID 5 uses parity, so it provides more usable storage capacity. Example: Four 1TB drives = 3TB usable. Other options are incorrect because: RAID 10 generally has excellent redundancy, often better than RAID 5. RAID 10 typically offers faster write speeds than RAID 5 because it does not calculate parity. RAID 10 also provides very good read performance.
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acf9805 👍 1 Answered A498. A — Less capacity 🧸 RAID 10 uses half its drives for mirrored copies, so you sacrifice more usable storage capacity.
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