RAID 10 vs RAID 5 Capacity Downside
Which of the following is a potential downside of using a RAID 10 configuration instead of a RAID 5 configuration?
Community Insight
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.
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.
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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
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?
RAID 10 writes directly to mirrored drives with no parity calculation, while RAID 5 incurs a read-modify-write parity penalty. RAID 10 therefore delivers faster, not slower, writes.
How much usable capacity does RAID 10 give compared to RAID 5?
RAID 10 always yields 50% of raw capacity because each drive is mirrored. RAID 5 yields (n−1)/n — for example, about 75% with four drives — so it packs more usable space.
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