RAID 10 for NAS: Mirror-Stripe, Capacity, and Speed vs Redundancy
RAID 10 combines the redundancy of RAID 1 (mirroring) with the performance of RAID 0 (striping). It delivers the best sequential read and write performance of any redundant RAID type. At the cost of 50% capacity efficiency.
See exactly how much usable storage your configuration delivers.
How RAID 10 Works
RAID 10 creates pairs of mirrored drives, then stripes data across all pairs. With four drives: drives 1 and 2 form a mirror, drives 3 and 4 form a mirror. Data is striped across the two mirror pairs. Reads can come from all four drives in parallel; writes go to both drives in each pair simultaneously.
Capacity Formula
Usable = n/2 × smallest drive capacity (50% of total, always)
- 4 × 4TB RAID 10: 2 × 3.64 TiB = 7.28 TiB raw
- 4 × 8TB RAID 10: 2 × 7.28 TiB = 14.55 TiB raw
- 8 × 4TB RAID 10: 4 × 3.64 TiB = 14.55 TiB raw
RAID 10 always requires an even number of drives (4, 6, 8…). Usable capacity is always exactly half the total. The same as RAID 6 on a 4-drive array, but with very different characteristics.
Performance Comparison
| RAID 5 | RAID 6 | RAID 10 | |
|---|---|---|---|
| Sequential read | Fast (all drives) | Fast (all drives) | Fast (all drives) |
| Sequential write | Moderate (parity overhead) | Slower (double parity) | Fast (no parity calc) |
| Random write | Slow | Slower | Fast |
| Rebuild time | Slow (reads all drives) | Slow | Fast (copies mirror pair) |
When to Choose RAID 10
- Database workloads: High random write IOPS with redundancy
- Video editing: Sustained sequential writes to multiple streams
- When rebuild speed matters: RAID 10 rebuilds are fast and do not stress remaining drives as much as RAID 5/6 rebuilds
For most home NAS users (media streaming, backup, file sharing), RAID 5 offers better capacity efficiency with adequate performance. RAID 10's advantages are most relevant for write-intensive workloads.
Frequently Asked Questions
Can RAID 10 tolerate two drive failures?
Possibly. RAID 10 can tolerate two simultaneous drive failures as long as they are not from the same mirror pair. If both drives in a pair fail, data is lost. If one drive from each of two different pairs fails, the array survives. This makes RAID 10's failure tolerance configuration-dependent, unlike RAID 6 which always tolerates any two failures.
Why does RAID 10 have the same usable capacity as RAID 6 on 4 drives?
On a 4-drive array, both RAID 6 and RAID 10 give 50% capacity efficiency. 2 drives of usable space from 4 drives. The key difference is performance: RAID 10 has faster random writes (no parity calculation) and faster rebuilds. RAID 6 provides guaranteed two-drive failure tolerance regardless of which drives fail.