Invention & History
- Introduced: Concept formalized in 1987 by David A. Patterson, Garth Gibson, and Randy Katz at the University of California, Berkeley.
- Original Paper: “A Case for Redundant Arrays of Inexpensive Disks (RAID)”.
- Purpose: RAID 5 was developed to provide a balance of performance, fault tolerance, and storage efficiency, filling the gap between RAID 0 (no fault tolerance) and RAID 1 (high redundancy but poor storage efficiency).
How RAID 5 Works
RAID 5 combines data striping (like RAID 0) with distributed parity for redundancy.
- Data and parity information are split and stored across at least three disks.
- Parity is not stored on a single disk, but is distributed across all drives to avoid bottlenecks.
- If one disk fails, the data can be reconstructed using the parity information from the remaining disks.
- Writes involve reading existing data blocks to calculate new parity, making writes slightly slower.
- Reads are very fast since data is striped across multiple disks.
🔁 Example Layout (with 3 disks):
| Stripe | Disk 1 | Disk 2 | Disk 3 |
|---|---|---|---|
| 1 | Data A1 | Data A2 | Parity A |
| 2 | Data B1 | Parity B | Data B2 |
| 3 | Parity C | Data C1 | Data C2 |
RAID 5 Features
| Feature | Value |
|---|---|
| Minimum Disks | 3 |
| Maximum Disks | 16–32 (varies by controller/OS) |
| Redundancy | ✅ Yes (1-disk fault tolerance) |
| Fault Tolerance | ✅ Yes (1 disk can fail safely) |
| Read Performance | ✅ Very High |
| Write Performance | ⚠️ Moderate due to parity calculations |
| Usable Capacity | (N – 1) * size_of_smallest_disk |
| Hot Swap Support | ✅ Yes |
| Rebuild Time | ⚠️ Long (depends on size & load) |
| Suitable for Boot? | ✅ Yes (with hardware RAID) |
Advantages
- Efficient Storage: Only one disk’s worth of capacity is used for parity, unlike RAID 1 which mirrors everything.
- Fault Tolerant: Can tolerate one disk failure without data loss.
- Read Performance: Excellent for read-heavy workloads due to striping.
- Cost-Effective: Provides redundancy with much better disk utilization than RAID 1.
- Scalable: Can add more disks to increase storage (with some limitations).
Disadvantages
- Write Penalty: Write speed is slower than RAID 0 or RAID 1 due to parity calculation overhead.
- Rebuild Time: Rebuilding a failed disk can take hours or even days, during which performance degrades and risk increases.
- Not Ideal for Heavy Writes: Not suited for databases or applications with frequent small write operations.
- Single Point of Failure: If another disk fails during rebuild, all data is lost.
Operating System Support
| Operating System | Supports RAID 5? | Tools/Notes |
|---|---|---|
| Linux | ✅ Yes | mdadm, LVM RAID, Btrfs (limited) |
| Windows | ✅ Yes | Storage Spaces or via hardware |
| macOS | ❌ No native | Not natively supported |
| FreeBSD | ✅ Yes | graid, zraid, vinum |
| NAS Systems | ✅ Yes | Synology, QNAP, FreeNAS/TrueNAS |
Hardware RAID Controllers
Most enterprise-grade controllers (e.g., LSI, Dell PERC, HP Smart Array) support RAID 5. Features include:
- Battery-backed write cache
- Hot-swapping support
- Dedicated parity offloading
- RAID migration tools
Example Commands (Linux Software RAID with mdadm)
# Create RAID 5 array with 3 disks
sudo mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sd[b-d]
# Format the array
sudo mkfs.ext4 /dev/md0
# Mount the array
sudo mkdir /mnt/raid5
sudo mount /dev/md0 /mnt/raid5
# Save configuration
sudo mdadm --detail --scan >> /etc/mdadm/mdadm.conf
Usage Scenarios
- File servers (SMB, NFS)
- Web servers
- Archival storage
- Virtualization hosts (with fast cache)
- Media storage (e.g., Plex, Jellyfin)
- On-prem NAS for homes and small offices
Summary Table
| Criteria | RAID 5 Value |
|---|---|
| Fault Tolerance | ✅ 1 Disk |
| Storage Efficiency | ✅ ~66–94% (depending on total disks) |
| Read Performance | ✅ Excellent |
| Write Performance | ⚠️ Moderate |
| Cost Efficiency | ✅ Better than RAID 1 |
| Ideal For | Read-heavy workloads, NAS, file/web servers |
Conclusion
RAID 5 offers an excellent balance between performance, storage efficiency, and fault tolerance, making it one of the most commonly used RAID levels in both enterprise and home environments. Its ability to withstand a single disk failure while maintaining high read speeds and relatively good storage utilization makes it ideal for applications that are read-intensive and where data redundancy is essential but budgets are limited.
However, RAID 5 does have limitations — particularly with write performance and rebuild time. As disk sizes continue to grow, rebuilds can take many hours or even days, increasing the risk of a second disk failure, which RAID 5 cannot tolerate. This is why RAID 6 or RAID 10 may be considered in environments where data integrity is critical and uptime must be maintained at all costs.
In short, RAID 5 remains a strong choice when you need a cost-effective storage solution that provides redundancy, high read throughput, and efficient disk usage, as long as you’re aware of its limitations and have monitoring and alerting in place to detect failures quickly.