RAID ( REDUNDANT ARRAY OF INDEPENDENT DISK)
What is RAID?
RAID is a data storage virtualization technology that combines multiple physical hard drives into one logical unit for:
- Redundancy (fault tolerance),
- Performance, or
- Both.
There are different RAID levels, each designed for specific needs.
Common RAID Levels Explained:
RAID 0 – Striping
- How it works: Data is split across multiple drives.
- Minimum drives: 2
- Fault tolerance: No redundancy.
Advantages:
- High read/write performance
- Utilizes full capacity of all drives
Disadvantages:
- If one drive fails, all data is lost
- No data protection
RAID 1 – Mirroring
- How it works: Data is duplicated (mirrored) across two or more drives.
- Minimum drives: 2
- Fault tolerance: Yes (1 drive failure)
Advantages:
- High read speed
- Simple setup
- Excellent data protection
Disadvantages:
- Storage capacity is halved
- Write performance slightly reduced
RAID 5 – Striping with Parity
- How it works: Data and parity (error correction info) are spread across all drives.
- Minimum drives: 3
- Fault tolerance: Can survive 1 drive failure
Advantages:
- Efficient storage (only one drive used for parity)
- Good read performance
- Fault tolerance
Disadvantages:
- Slower write performance due to parity calculations
- Rebuild time after failure can be long
RAID 6 – Striping with Double Parity
- How it works: Similar to RAID 5 but stores two parity blocks.
- Minimum drives: 4
- Fault tolerance: Can survive 2 drive failures
Advantages:
- Higher fault tolerance than RAID 5
- Suitable for large arrays
Disadvantages:
- Slower writes than RAID 5
- More storage used for parity
- Longer rebuild times
RAID 10 (1+0) – Mirrored Stripes
- How it works: Combines RAID 1 and RAID 0. Data is mirrored, then striped.
- Minimum drives: 4
- Fault tolerance: Yes (can survive multiple failures in different mirror pairs)
Advantages:
- High performance and redundancy
- Fast recovery from failure
Disadvantages:
- Only 50% usable capacity
- More costly (requires more drives)
RAID 01 (0+1) – Striped Mirrors
- How it works: Opposite of RAID 10 – stripes two mirrored sets.
- Minimum drives: 4
- Fault tolerance: Less fault-tolerant than RAID 10
Advantages:
- High performance
- Some redundancy
Disadvantages:
Less reliable than RAID 10
If one mirror fails, whole array can be at risk
Common RAID Levels Explained:
| RAID Level | Min. Disks | Redundancy | Speed | Storage Efficiency | Key Benefit |
| RAID 0 | 2 | None | High | 100% | Speed |
| RAID 1 | 2 | Yes | Medium | 50% | Mirroring |
| RAID 5 | 3 | Yes | Good | 67–94% | Balanced |
| RAID 6 | 4 | Yes (2 disk failure) | Slower writes | 50–88% | Extra safety |
| RAID 10 | 4 | Yes | High | 50% | Speed + Redundancy |
RAID Levels Visual Diagram
Here’s a simple ASCII-style representation of each RAID level:
RAID 0 (Striping)
[Disk 1] A1 A3 A5
[Disk 2] A2 A4 A6
→ High speed, no redundancy
RAID 1 (Mirroring)
[Disk 1] A1 A2 A3
[Disk 2] A1 A2 A3
→ Data mirrored for redundancy
RAID 5 (Striping + Parity)
[Disk 1] A1 A2 P1
[Disk 2] A3 P2 A4
[Disk 3] P3 A5 A6
→ Can survive 1 disk failure
RAID 6 (Striping + Double Parity)
[Disk 1] A1 A2 P1 Q1
[Disk 2] A3 P2 A4 Q2
[Disk 3] P3 A5 Q3 A6
[Disk 4] Q4 Q5 P4 P5
→ Can survive 2 disk failures
RAID 10 (RAID 1 + RAID 0)
Mirror 1: [Disk 1] A1 A2 | [Disk 2] A1 A2
Mirror 2: [Disk 3] B1 B2 | [Disk 4] B1 B2
→ Fast and fault-tolerant
Which One Should You Use?
| Use Case | Recommended RAID |
| Speed (non-critical data) | RAID 0 |
| Redundancy with small setup | RAID 1 |
| Best overall for most servers | RAID 5 |
| High fault tolerance (critical) | RAID 6 or RAID 10 |
