Invention Date & History
- Introduced: Early 2000s
- Developed By: Not attributed to a single company, but built upon the concepts of RAID 5.
- Published In: Expanded from the original RAID taxonomy paper (1987) by Patterson, Gibson, and Katz at the University of California, Berkeley.
- RAID 6 is often seen as an evolution of RAID 5, addressing its key weakness—protection against only one disk failure.
What is RAID 6?
RAID 6 (Redundant Array of Independent Disks, level 6) is a storage configuration that offers fault tolerance through double parity. It allows up to two simultaneous disk failures without losing data. RAID 6 stripes data and two sets of parity information across all disks.
It uses block-level striping with double distributed parity, and requires a minimum of 4 disks.
How RAID 6 Works
- Data is striped across all disks, similar to RAID 5.
- Two different parity blocks are written to two separate drives per stripe.
- The dual parity provides extra fault tolerance.
- If any two drives fail, the system can still reconstruct data using the parity info.
Features of RAID 6
- Double disk failure protection
- Block-level striping with dual parity
- Excellent read performance
- Moderate write performance (slower than RAID 5)
- Can survive multiple simultaneous disk failures
Advantages of RAID 6
| Advantage | Description |
|---|---|
| ✅ High Fault Tolerance | Survives 2 disk failures |
| ✅ Ideal for Large Arrays | Especially when using large-capacity drives |
| ✅ Read Speed | Comparable to RAID 5 or better |
| ✅ Reliability | Excellent for long-term storage needs |
| ✅ Data Safety | Ensures no data loss even if 2 drives fail simultaneously |
Disadvantages of RAID 6
| Disadvantage | Description |
|---|---|
| ❌ Slower Write Speed | Due to dual parity calculations |
| ❌ Storage Overhead | Requires more disk space for parity |
| ❌ Complex Rebuilds | Rebuilds after failure are longer and stress remaining drives |
| ❌ Requires More Disks | Minimum of 4 disks; recommended 6+ for efficiency |
RAID 6 Use Cases
- Enterprise NAS and SAN solutions
- Backup servers
- Data archiving
- Large-scale storage systems
- Media servers with high redundancy needs
- Cloud storage providers
- Scientific computing, where uptime and data reliability are critical
Operating System and Hardware Support
| Platform | Support |
|---|---|
| Linux | ✅ (mdadm, ZFS, Btrfs, etc.) |
| Windows | ✅ (via Storage Spaces or hardware RAID) |
| FreeBSD | ✅ |
| Hardware RAID Controllers | ✅ (LSI, Dell PERC, HP Smart Array, etc.) |
Create RAID 6 on Linux using mdadm (Software RAID)
Step-by-step:
# Step 1: Install mdadm if not already installed
sudo apt install mdadm
# Step 2: Create RAID 6 with 6 devices (e.g., /dev/sd[b-g])
sudo mdadm --create --verbose /dev/md0 --level=6 --raid-devices=6 /dev/sd[b-g]
# Step 3: Create filesystem
sudo mkfs.ext4 /dev/md0
# Step 4: Mount the RAID
sudo mkdir -p /mnt/raid6
sudo mount /dev/md0 /mnt/raid6
# Step 5: Save RAID configuration
sudo mdadm --detail --scan >> /etc/mdadm/mdadm.conf
Example Parameters to Monitor RAID 6:
# Check RAID status
cat /proc/mdstat
# Detailed information
sudo mdadm --detail /dev/md0
Storage Efficiency
| Total Drives | Usable Capacity |
|---|---|
| 4 Drives | 50% |
| 6 Drives | 66.7% |
| 10 Drives | 80% |
Usable capacity formula:
Usable = (N - 2) × size_of_smallest_disk
Conclusion
RAID 6 is a robust and reliable storage configuration that builds upon the strengths of RAID 5 by adding a second layer of parity, allowing it to survive two simultaneous disk failures without data loss. This makes it an ideal choice for large-capacity storage arrays, especially where uptime and data integrity are mission-critical — such as in enterprise servers, data centers, NAS/SAN environments, and backup systems.
Despite slower write performance due to dual parity calculations and increased complexity during disk rebuilds, the enhanced fault tolerance significantly outweighs these drawbacks in high-availability scenarios. RAID 6 ensures long-term data reliability and is especially valuable in environments using large-capacity or aging disks, where the probability of a second failure during rebuilds is higher.
In summary, RAID 6 offers a balanced compromise between redundancy and storage efficiency, and is a smart choice for organizations and professionals who prioritize data safety over raw performance.