RAID 10 Capacity Calculator
Calculate usable capacity of a RAID 10 striped-mirror array from disk count and size.
Inputs
Usable Capacity
4,000.00GB
Raw Capacity
8,000.00GB
Mirror Overhead
4,000.00GB
Storage Efficiency
50.00%
Fault Tolerance
Tolerates 1 failure per mirror pair
Step by step
Disk count (n, even)
4
= 4
Disk size
2000 GB
= 2000 GB
RAID 10 usable capacity
n/2 × size = 4/2 × 2000
= 4000 GB
Mirror pairs
n/2 = 2
= 2 pairs
Storage efficiency
50% (half for mirrors)
= 50%
How it works
RAID 10 combines mirroring (RAID 1) and striping (RAID 0) by creating mirrored pairs of disks, then striping data across those pairs. Usable capacity is exactly half the raw capacity. It offers both good random I/O performance (from striping) and redundancy (from mirroring), tolerating one disk failure per mirror pair without data loss.
Formula
RAID 10 usable capacity
usable = (n / 2) × disk_size
- n
- total disk count (even)
- S
- capacity per disk
Frequently Asked Questions
Why does RAID 10 require an even number of disks?
RAID 10 mirrors disks in pairs before striping across pairs, so each disk needs a partner — an odd number leaves one disk without a mirror, which most controllers do not allow.
Is RAID 10 faster than RAID 5?
For random writes, yes — RAID 10 has no parity calculation overhead, so write latency is lower. Read performance is comparable or slightly better due to mirror read splitting.