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Understanding RAID
RAID (Redundant Array of Independent Disks) combines multiple physical drives into a single logical storage unit. Different RAID levels offer varying trade-offs between performance, capacity, and fault tolerance.
RAID Levels Explained
RAID 0 (Striping): Data is split across all drives for maximum speed and capacity. ⚠️ NO redundancy—if one drive fails, all data is lost. Use for non-critical speed-heavy workloads (video editing scratch disks).
RAID 1 (Mirroring): All data is duplicated across drives. Excellent fault tolerance (can lose N-1 drives), but 50% capacity efficiency. Best for mission-critical data where uptime matters more than capacity.
RAID 5 (Striping + Parity): Data is striped with distributed parity. Can survive 1 drive failure. Requires minimum 3 drives. Capacity efficiency improves with more drives (e.g., 4 drives = 75%, 6 drives = 83.3%). Good balance for file servers.
RAID 6 (Dual Parity): Like RAID 5 but with dual parity—can survive 2 simultaneous drive failures. Requires minimum 4 drives. Safer than RAID 5, especially with large drives (reduces rebuild risk). Recommended for enterprise storage.
RAID 10 (Mirroring + Striping): Combines RAID 1 and RAID 0. Requires at least 4 drives (even number). 50% capacity efficiency, but excellent performance and fault tolerance. Can survive multiple drive failures (as long as no mirrored pair is lost). Ideal for databases.
💡 Expert Tip: RAID 10 for Databases
For database servers (MySQL, PostgreSQL, SQL Server), RAID 10 is often the best choice. It offers excellent read/write performance, better than RAID 5/6, and can handle many simultaneous small I/O operations. The 50% capacity cost is worth it for the speed and reliability boost in transaction-heavy workloads.
⚠️ Common Mistake: RAID Is NOT Backup!
RAID protects against hardware failure, not data loss from accidental deletion, ransomware, corruption, or fire/theft. You MUST have separate backups (3-2-1 rule: 3 copies, 2 different media, 1 offsite). RAID + backups = proper data protection strategy.
Quick Comparison Table
| RAID Level | Min Drives | Fault Tolerance | Capacity Efficiency |
|---|---|---|---|
| RAID 0 | 2 | None | 100% |
| RAID 1 | 2 | N-1 drives | 50% |
| RAID 5 | 3 | 1 drive | (N-1)/N |
| RAID 6 | 4 | 2 drives | (N-2)/N |
| RAID 10 | 4 (even) | Multiple* | 50% |
*RAID 10 can survive multiple drive failures as long as no mirrored pair is completely lost.
Reviewed by: Kevin Zhang, Storage Engineer
Last updated: November 27, 2025
Frequently Asked Questions
What is RAID?
RAID stands for Redundant Array of Independent Disks. It's a technology that combines multiple physical hard drives into a single logical unit for improved performance, data redundancy, or both.
Which RAID level is best for data protection?
RAID 6 offers the best protection against drive failures, as it can survive two simultaneous disk failures thanks to dual parity. RAID 1 (mirroring) is also excellent but uses 50% of total capacity.
How much usable space do I get with RAID 5?
In RAID 5, one drive's worth of capacity is used for parity data. With 4×4TB drives (16TB total), you get 12TB usable (75% efficiency). The more drives, the better the efficiency.
What's the difference between RAID 5 and RAID 6?
RAID 5 uses one drive for parity (can survive 1 drive failure), while RAID 6 uses two drives for dual parity (can survive 2 simultaneous drive failures). RAID 6 is safer but sacrifices more capacity.