RAID Capacity
Calculate usable capacity across RAID 0, 1, 5, 6 and 10 configurations.
Inputs
Usable Capacity
20.00TB
Raw Capacity
24.00TB
Storage Efficiency
83.3%
Parity/Mirror Overhead
4.00TB
Drive Failures Tolerated
1
Step by step
Raw capacity
6 * 4 TB
= 24 TB
Usable capacity (RAID ${raidLevel})
(6 - 1) * 4
= 20 TB
Storage efficiency
20 / 24 * 100
= 83.3%
Drive failures tolerated
RAID 5 fault tolerance
= 1
How it works
RAID levels trade capacity for redundancy. RAID 0 offers full capacity but zero fault tolerance. RAID 1 mirrors all data (50% efficiency for 2 drives). RAID 5 uses one drive's worth for distributed parity (n-1 efficiency). RAID 6 uses two drives for double parity. RAID 10 stripes across mirror pairs (50% efficiency).
Formulas
RAID 5 usable capacity
usable = (drives - 1) * drive_size
- n
- Number of drives
- S
- Size per drive
RAID 6 usable capacity
usable = (drives - 2) * drive_size
Frequently Asked Questions
Which RAID level should I choose?
RAID 5 balances capacity and protection for most workloads. RAID 6 is preferred for large arrays (>4 drives) where rebuild times are long enough to risk a second failure. RAID 10 is best for write-intensive workloads needing both performance and redundancy. RAID 0 is only appropriate when data loss is acceptable.
Why is RAID not a substitute for backups?
RAID protects against drive failure only. It cannot protect against accidental deletion, corruption, ransomware, controller failure, or disasters affecting the entire array. Backups protect against all of these scenarios.