Miscellaneous - RAID
💾 RAID — Redundant Array of Independent Disks
RAID is a technology that combines multiple physical storage devices (HDDs or SSDs) into one logical storage system to improve performance, reliability, or both.
1️⃣ What is RAID?
RAID = Redundant Array of Independent Disks
It allows multiple drives to act like:
- One logical disk
- With improved speed, fault tolerance, or data safety
Main Goals
✔ Higher performance
✔ Data redundancy (backup)
✔ Fault tolerance
✔ Larger logical storage
2️⃣ Key RAID Concepts
🔹 Striping
Splitting data across multiple disks for higher speed
1
2
Disk 1 → A1 A3 A5
Disk 2 → A2 A4 A6
✔ Faster read/write
❌ No redundancy
🔹 Mirroring
Storing exact copies of data on multiple disks
1
2
Disk 1 → DATA
Disk 2 → DATA (Copy)
✔ High reliability
❌ Storage efficiency reduced
🔹 Parity
Extra information used to detect and recover lost data
✔ Saves space compared to full copies
✔ Allows data recovery if a disk fails
3️⃣ RAID Levels Overview
🟦 RAID 0 — Striping (Performance)
How it Works
- Data is striped across disks
- No redundancy
Pros
✔ Very fast I/O
✔ Full storage utilization
Cons
❌ No fault tolerance
❌ One disk failure = data loss
Use Case
Gaming PCs, temporary storage, scratch disks
🟩 RAID 1 — Mirroring (Reliability)
How it Works
- Data is fully duplicated
- Every disk holds a copy
Pros
✔ High reliability
✔ Fast reads
Cons
❌ Storage capacity = 50%
❌ Higher cost
Use Case
Critical data backups, OS disks
🟨 RAID 4 — Dedicated Parity Disk
How it Works
- Data striped across disks
- One dedicated disk stores parity
Pros
✔ Better capacity efficiency than RAID 1
✔ Can recover from one disk failure
Cons
❌ Parity disk bottleneck on writes
🟧 RAID 5 — Distributed Parity (Single Parity)
How it Works
- Data striped across disks
- Parity distributed across all disks
Pros
✔ No single parity bottleneck
✔ Survives 1 disk failure
✔ Good balance of speed & safety
Cons
❌ Write performance overhead
❌ Rebuild time can be long
Common Use
File servers, NAS, enterprise storage
🟥 RAID 6 — Distributed Dual Parity
How it Works
- Like RAID 5, but stores two parity blocks
- Survives 2 disk failures
Pros
✔ Higher fault tolerance than RAID 5
✔ Safer for large arrays
Cons
❌ Slower writes than RAID 5
❌ More storage overhead
Common Use
Enterprise storage, large-scale servers
4️⃣ RAID Level Comparison
| RAID | Min Disks | Performance | Redundancy | Usable Capacity |
|---|---|---|---|---|
| RAID 0 | 2 | ⭐⭐⭐⭐ | ❌ None | 100% |
| RAID 1 | 2 | ⭐⭐ | ✅ High | 50% |
| RAID 4 | 3 | ⭐⭐ | ✅ 1 disk | (N-1)/N |
| RAID 5 | 3 | ⭐⭐⭐ | ✅ 1 disk | (N-1)/N |
| RAID 6 | 4 | ⭐⭐ | ✅ 2 disks | (N-2)/N |
5️⃣ Performance vs Reliability Tradeoff
| RAID Level | Best For |
|---|---|
| RAID 0 | Maximum speed |
| RAID 1 | Maximum safety |
| RAID 5 | Balanced performance & safety |
| RAID 6 | High safety for large arrays |
6️⃣ RAID Is NOT a Backup
RAID protects against disk failure,
but NOT against:
❌ Accidental deletion
❌ Malware / ransomware
❌ File corruption
❌ Fire / theft
📌 Always use separate backups
7️⃣ Developer Takeaways
✔ RAID 0 = fast but unsafe
✔ RAID 1 = safe but storage inefficient
✔ RAID 5 = most common balanced option
✔ RAID 6 = safer for large storage pools
✔ RAID improves availability, not data correctness
🧩 One-Line Mental Model
RAID spreads data across disks to gain speed, safety, or both.