RAID 0, 1, 5, 6, 10: Which Configuration Protects Your Data Best?
Not all RAID configurations are equally safe. Choosing a RAID level is always a compromise between performance, capacity, and data protection. The wrong choice can cost you data, time, and money.
In this article, we'll compare the most commonly used RAID configurations from the perspective of security, performance, and data recovery complexity.
RAID 0 – Striping Without Redundancy
How It Works
Data is divided into blocks (stripes) and distributed alternately across all disks. No redundancy, no parity.
Example with 4 disks:
- Block 1 → Disk 1
- Block 2 → Disk 2
- Block 3 → Disk 3
- Block 4 → Disk 4
- Block 5 → Disk 1
- ...
Advantages
Maximum performance: Reading and writing occurs in parallel on all disks. Theoretical performance = number of disks × performance of one disk.
100% capacity utilization: All disks contribute their full capacity. 4× 2TB = 8TB.
Simple implementation: No overhead for parity or mirroring.
Disadvantages
NO protection: Failure of any disk = loss of ALL data. Probability of failure increases with the number of disks.
Higher risk: More disks = higher probability that one will fail. RAID 0 with 8 disks has 8× higher chance of data loss than a single disk.
When to Use
- Temporary data (cache, scratch disk)
- Rendering, video editing (with separate backup)
- Gaming setups (where data loss doesn't matter)
NEVER for:
- Important data
- Production servers
- Anything without backup
Data Recovery from RAID 0
Difficulty: High to extreme
After disk failure, data is scattered in blocks that cannot be assembled without the missing disk. Recovery success depends on whether the failed disk can be read.
Success rate: 30-50%
RAID 1 – Mirroring
How It Works
Identical copy of data on two (or more) disks. Every write goes to both disks simultaneously.
Example with 2 disks:
- Data A → Disk 1 + Disk 2
- Data B → Disk 1 + Disk 2
Advantages
Simple redundancy: One disk can fail and data is still available on the other.
Fast reading: Controller can read from both disks in parallel.
Easy recovery: When one disk fails, simply connect the other as a standalone disk.
Fast rebuild: 1:1 copying is faster than parity calculation.
Disadvantages
50% capacity utilization: Half the capacity goes to mirroring. 2× 2TB = 2TB usable.
Slower writes: Every write must occur on both disks.
When to Use
- System disks (boot drives)
- Small servers with critical data
- Situations where simplicity is more important than capacity
Data Recovery from RAID 1
Difficulty: Lowest of all RAID
If one disk fails, the other contains complete data. Even with both disks failing, chances are high – just need to recover one.
Success rate: 90-99%
RAID 5 – Striping with Parity
How It Works
Data is distributed across disks (striping) + one parity block for each stripe. Parity is distributed alternately across all disks.
Example with 4 disks:
- Stripe 1: A1, A2, A3, Parity(A) → Disk 1, 2, 3, 4
- Stripe 2: B1, B2, Parity(B), B3 → Disk 1, 2, 3, 4
- ...
Parity allows calculating the missing block when one disk fails.
Advantages
Good compromise: Combines performance, redundancy, and capacity.
Efficient capacity utilization: (n-1)/n – with 4 disks, 75% capacity is utilized. 4× 2TB = 6TB usable.
High read performance: Parallel reading from multiple disks.
Disadvantages
Tolerates only 1 disk failure: Failure of 2 disks = data loss.
Slower writes: Every write requires parity calculation.
URE risk during rebuild: With large disks, there's a high probability of Unrecoverable Read Error during rebuild.
When to Use
- File servers for small to medium businesses
- NAS for SMB
- Situations where capacity is more important than maximum security
Caution: RAID 5 with large disks (8TB+) is risky. Consider RAID 6.
Data Recovery from RAID 5
Difficulty: Medium
Requires correct determination of disk order, stripe size, and parity rotation. With one failed disk, recovery is usually successful. With two failed disks, it's more complex.
Success rate: 70-90%
RAID 6 – Double Parity
How It Works
Similar to RAID 5, but with two independent parity blocks for each stripe. Uses two different algorithms (P and Q).
Example with 6 disks:
- Stripe: D1, D2, D3, D4, P, Q → distributed across all 6 disks
Advantages
Tolerates 2 disk failures: Major advantage over RAID 5, especially with larger arrays.
Safer rebuild: During rebuild after 1 disk failure, you still have a reserve of 1 disk.
Suitable for large disks: Statistically higher chance of successful rebuild than RAID 5.
Disadvantages
Slower writes: Calculating two parities is more demanding.
Less capacity: (n-2)/n – with 6 disks, 67% is utilized. 6× 2TB = 8TB usable.
Longer rebuild: Calculating two parities takes longer.
When to Use
- Large arrays (8+ disks)
- Enterprise storage
- Critical data where security is important
- NAS with large disks (4TB+)
Data Recovery from RAID 6
Difficulty: Medium to higher
Two parity algorithms complicate reconstruction but also provide better chances of recovery during disk failures.
Success rate: 80-95%
RAID 10 (1+0) – Mirror + Stripe
How It Works
Combination of RAID 1 and RAID 0. First, mirrored pairs are created, then striping is performed across them.
Example with 4 disks:
- Pairs: Disk 1+2 (mirror), Disk 3+4 (mirror)
- Striping across both pairs
Advantages
High performance: Reading and writing is fast – combines advantages of striping and mirroring.
Good redundancy: Each mirror pair can survive failure of one disk.
Fast rebuild: Rebuild is only copying within the mirror pair.
Disadvantages
50% capacity utilization: Half goes to mirroring. 4× 2TB = 4TB usable.
Higher costs: You need 2× more disks for the same capacity.
Depends on which disks fail: Failure of both disks in the same pair = data loss.
When to Use
- Databases (SQL Server, Oracle, MySQL)
- Virtualization
- High-performance applications
- Situations where performance is critical
Data Recovery from RAID 10
Difficulty: Medium
Depends on which disks failed. If both disks of one pair, the situation is more complex.
Success rate: 75-95%
Comparison Table
| RAID | Min. disks | Resilience | Capacity | Read | Write | Recovery |
|---|---|---|---|---|---|---|
| 0 | 2 | None | 100% | Excellent | Excellent | Difficult |
| 1 | 2 | 1 disk | 50% | Good | Medium | Easy |
| 5 | 3 | 1 disk | (n-1)/n | Excellent | Medium | Medium |
| 6 | 4 | 2 disks | (n-2)/n | Excellent | Worse | Medium |
| 10 | 4 | 1/mirror | 50% | Excellent | Good | Medium |
Our Recommendations by Situation
Small Business (up to 20 employees)
RAID 1 for system disk, RAID 5 or 6 for data.
Plus: Regular backups to external storage or cloud.
Medium Business (20-100 employees)
RAID 6 or RAID 10 depending on priorities (capacity vs performance).
Plus: Backups, monitoring, documentation, hot spare.
Enterprise
RAID 6 + hot spare for data storage, RAID 10 for databases.
Plus: Professional monitoring, regular backup testing, disaster recovery plan.
Always Remember
No RAID replaces backup. RAID protects against disk failure, not against:
- Ransomware
- Human error
- Fire, flood
- Multiple disk failures simultaneously
Hardware vs Software RAID
Hardware RAID
- Standalone controller (Dell PERC, HP Smart Array)
- Dedicated processor for RAID operations
- Faster, but dependent on specific hardware
Software RAID
- OS-controlled (Windows Storage Spaces, Linux mdadm, ZFS)
- Uses server CPU
- More flexible, hardware-independent
Security Impact
Hardware RAID:
- Controller failure can make data inaccessible
- Requires compatible replacement controller
- Metadata often proprietary
Software RAID:
- Disks portable between systems
- Metadata usually standardized
- Dependent on functional OS
FAQ
Which RAID is safest?
In terms of protection against disk failure: RAID 6 (tolerates 2 failures) or RAID 10 (high redundancy + performance).
But remember: No RAID protects against all risks. Backup is essential.
Can I change RAID level?
Sometimes yes, depends on controller and RAID type. Some controllers allow online migration (e.g., RAID 5 → RAID 6). Always backup before making changes.
How many disks do I need?
| RAID | Minimum | Recommended |
|---|---|---|
| 0 | 2 | 2-4 |
| 1 | 2 | 2 |
| 5 | 3 | 4-6 |
| 6 | 4 | 6-8 |
| 10 | 4 | 4-8 |
Is RAID 5 dangerous?
With large disks (8TB+) yes. Probability of URE during rebuild is high. For large disks, we recommend RAID 6.
What is hot spare?
A spare disk connected to the array that automatically replaces a failed disk. Shortens degraded state time but doesn't eliminate rebuild risks.
Need Help Choosing RAID?
Or do you have an existing RAID that needs recovery? We're happy to help.
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