Storage, made clear
RAID 6 Calculator
Estimate usable storage with double-parity protection. RAID 6 requires at least four drives.
Estimated usable RAID capacity
≈ 14.55 TiB
4 × 8 TB drives in RAID 6
- Raw capacity
- 32 TB
- RAID overhead
- 16 TB
- Storage efficiency
- 50%
- Fault tolerance
- 2 drives
Multiple drive failures may be tolerated if they occur in different mirror pairs.
Estimated RAID-level capacity. Formatting, filesystem metadata and system reservations can reduce the space available for files.
Check your array configuration
Correct the input to see an estimated usable capacity.
Building this RAID array?
You’ll need 4 × 8 TB drives.
Compare RAID levels
| RAID | Usable capacity | Efficiency | Protection |
|---|
Mirror-based protection depends on which drives fail. RAID 10 tolerates at least one drive failure.
Example RAID 6 capacities
| Drives | Raw | Usable | Binary usable |
|---|---|---|---|
| 4 × 8 TB | 32 TB | 16 TB | 14.55 TiB |
| 6 × 8 TB | 48 TB | 32 TB | 29.10 TiB |
| 8 × 8 TB | 64 TB | 48 TB | 43.66 TiB |
How RAID 6 capacity is calculated
At least 4 drives. The equivalent of two drives’ capacity is used for distributed parity. Usable capacity is (N − 2) × drive size, with tolerance for 2 drive failures.
RAID 6 requirements
Use at least 4 equal-capacity drives. RAID 6 tolerates two drive failures; additional failures can cause data loss.
RAID 6 advantages and limitations
RAID 6 adds a second layer of parity and can tolerate two drive failures. Its capacity overhead is equivalent to two drives. It gives more failure tolerance than RAID 5, but less usable capacity for the same drive count and additional parity write work.
RAID 6 examples
With four 8 TB drives, RAID 6 provides 16 TB usable from 32 TB raw. With eight 8 TB drives, it provides 48 TB usable from 64 TB raw. In both cases, two drives’ worth of capacity is used for parity.
Frequently asked questions
How many drives does RAID 6 require?
Use at least 4 equal-capacity drives. RAID 6 tolerates two drive failures; additional failures can cause data loss.
How is RAID 6 usable capacity calculated?
(Number of drives − 2) × capacity per drive. All drives are assumed to have the same capacity.
How many drive failures can RAID 6 tolerate?
Two drive failures. Keep separate backups because RAID does not protect against every cause of data loss.
Does RAID 6 replace a backup?
No. Separate backups are needed for accidental deletion, malware, theft, fire and other risks.
Why does my RAID 6 array show less space in my operating system?
Your operating system may display binary units. Formatting, filesystem metadata and system reservations can also reduce available space.
Choosing a layout? Compare all RAID levels, or try RAID 5, RAID 10.