Raid6 Calculator
Building a RAID 6 storage array? Understanding how much usable storage you’ll have—and what you’ll lose to redundancy—is essential. The RAID 6 Calculator on our site helps you plan your storage with confidence by giving you fast, accurate results based on the number and size of your disks.
This article will walk you through how to use the tool, offer real-world examples, and answer the most common questions users have about RAID 6 storage planning.
What Is RAID 6?
RAID 6 (Redundant Array of Independent Disks) is a fault-tolerant storage configuration that can withstand two simultaneous disk failures. It achieves this by storing two blocks of parity data across the array. This makes RAID 6 highly suitable for environments where data integrity and uptime are critical.
However, this redundancy comes at the cost of usable storage capacity. That’s where the RAID 6 Calculator comes in—it helps you determine:
- Total raw storage capacity
- Usable storage capacity (after parity)
- Space reserved for parity
- Disk failure tolerance
How to Use the RAID 6 Calculator (Step-by-Step)
1. Enter the Number of Disks
Start by inputting how many disks you plan to include in your RAID 6 array. Minimum is 4, maximum supported by the tool is 24.
2. Enter Disk Size
Specify the storage capacity of each disk. For example, if you’re using 4 TB drives, type 4.
3. Select the Size Unit (GB or TB)
Choose whether your disk size is measured in gigabytes (GB) or terabytes (TB). The calculator will automatically convert sizes if necessary.
4. Click “Calculate”
After filling in your inputs, press Calculate. Your results will appear below, showing your:
- Total capacity
- Usable space
- Parity overhead
- Fault tolerance (always 2 disks for RAID 6)
5. Use “Reset” to Start Over
If you want to try different values, click Reset to clear all inputs and outputs.
Real-World Example: Planning a RAID 6 Array
Let’s say you’re configuring a RAID 6 setup with:
- 8 disks, each 4 TB
Here’s what the calculator will show:
- Total Capacity: 32 TB
- Usable Capacity: 24 TB
- Parity Space: 8 TB
- Failure Tolerance: Can survive 2 disk failures
- Storage Efficiency: 75%
This means 25% of your raw capacity is used for redundancy, and 75% is available for storage—an expected trade-off for strong fault tolerance.
Use Cases for RAID 6
RAID 6 is particularly effective in the following environments:
- Enterprise NAS Systems – Protect sensitive data across multiple disks.
- Media Servers – Safeguard against data loss while maintaining large file access.
- Virtual Machine Hosts – Ensure VM stability even during hardware failure.
- Backup Archives – Store large volumes of historical data with extra fault protection.
- SMBs and IT Departments – Balance performance, capacity, and redundancy.
RAID 6 is slower than RAID 5 for write operations but offers higher protection. If data integrity matters more than write speed, RAID 6 is a solid choice.
RAID 6 Storage Efficiency Guide
| Number of Disks | Usable Disks | Storage Efficiency |
|---|---|---|
| 4 | 2 | 50% |
| 6 | 4 | 66.7% |
| 8 | 6 | 75% |
| 12 | 10 | 83.3% |
| 16 | 14 | 87.5% |
| 24 | 22 | 91.7% |
As shown, the more disks you use, the higher your storage efficiency in RAID 6.
17 RAID 6 FAQs (Frequently Asked Questions)
1. What is the minimum number of disks required for RAID 6?
You need at least 4 disks to create a RAID 6 array. Two are used for parity.
2. Why does RAID 6 use two disks for parity?
This allows the array to tolerate two simultaneous disk failures, improving data safety.
3. What happens if more than two disks fail?
If 3 or more disks fail in RAID 6, the array fails and data recovery becomes extremely difficult or impossible without a backup.
4. Can I mix disk sizes in RAID 6?
Technically yes, but the array will use the size of the smallest disk across all drives. This leads to wasted space.
5. What’s the usable capacity formula for RAID 6?
(Number of Disks – 2) × Disk Size = Usable Capacity
6. Is RAID 6 better than RAID 5?
Yes, RAID 6 is more fault-tolerant than RAID 5, but slightly slower due to extra parity calculations.
7. What’s the trade-off with RAID 6?
You lose the capacity of two disks to redundancy, and write performance may be lower than simpler RAID levels.
8. Can I expand a RAID 6 array later?
Some RAID controllers and software (like ZFS or UnRAID) allow expansion, but it often requires rebuilding the array.
9. How much storage space is used for parity in RAID 6?
Exactly two disks’ worth of space is dedicated to parity data, regardless of total disk count.
10. What is RAID 6 storage efficiency?
Storage efficiency is the percentage of total space that’s usable. Formula:Usable Capacity / Total Capacity × 100
11. Is RAID 6 good for home use?
It can be, especially if you’re storing important data or backups, but might be overkill for casual use.
12. Is RAID 6 fault-tolerant?
Yes, RAID 6 is designed for high fault tolerance, surviving up to 2 disk failures.
13. What is the performance impact of RAID 6?
Write speeds are slower due to the need to calculate two sets of parity. Read performance remains strong.
14. Can I use SSDs in a RAID 6 array?
Yes, but ensure your RAID controller or software supports TRIM and wear leveling for SSDs.
15. How does RAID 6 compare to RAID 10?
- RAID 6: Better storage efficiency, higher redundancy
- RAID 10: Faster performance, but less efficient (50% storage loss)
16. What file system works best with RAID 6?
ZFS, EXT4, and Btrfs are commonly used. ZFS also adds built-in checksums and data integrity features.
17. Do I still need backups with RAID 6?
Absolutely. RAID protects against hardware failure, not against accidental deletion, corruption, or ransomware.
Final Thoughts
RAID 6 is one of the most robust RAID levels for both personal and enterprise use, offering a smart balance between redundancy and usable capacity. With our RAID 6 Calculator, you can easily determine how much usable storage you’ll get from your chosen disk configuration—without needing to do manual math or risk overestimating your space.
Whether you’re planning your first NAS build or expanding a large-scale archive, this calculator simplifies the technical side so you can focus on building reliable, fault-tolerant storage.
Try the RAID 6 Calculator now and plan your storage like a pro.