RAID 1 Capacity Calculator
Calculate usable capacity of a RAID 1 mirrored array from disk count and size.
Inputs
Usable Capacity
2,000.00GB
Raw Capacity
4,000.00GB
Mirror Overhead
2,000.00GB
Storage Efficiency
50.00%
Fault Tolerance
Tolerates 1 disk failure(s)
Step by step
Disk count (n)
2
= 2
Disk size
2000 GB
= 2000 GB
RAID 1 usable capacity
disk_size = 2000
= 2000 GB
Fault tolerance
n - 1 = 1
= 1 disk failure(s)
Storage efficiency
1/n × 100 = 1/2 × 100
= 50%
How it works
RAID 1 mirrors identical copies of data across all disks in the array, so usable capacity equals a single disk's size regardless of how many mirrors exist. The trade-off is maximum redundancy — all disks minus one can fail without data loss — at the cost of the lowest storage efficiency of any standard RAID level.
Formulas
RAID 1 usable capacity
usable = disk_size (one disk's worth regardless of mirror count)
- S
- capacity of each disk
Storage efficiency
efficiency = 1/n × 100%
- n
- number of mirrored disks
Frequently Asked Questions
Can RAID 1 have more than 2 disks?
Yes. A 3-way or even 4-way mirror is possible — usable capacity stays at one disk's size, but fault tolerance increases to n-1 simultaneous failures.
Does RAID 1 improve read performance?
Read throughput can improve because the controller can read from multiple mirrors in parallel. Write performance does not improve because every write must be committed to all mirrors.