What Is RAID?
RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple physical disk drives into one or more logical units for data redundancy, performance improvement, or both. RAID is widely used in servers, NAS devices, and workstations to protect against disk failure and improve I/O performance.
Different RAID levels offer different tradeoffs between performance, capacity, and redundancy. Choosing the right RAID level depends on your priorities: maximum speed (RAID 0), maximum protection (RAID 1, 6, 10), or a balance of both (RAID 5).
RAID Capacity Formulas
RAID Level Comparison
| RAID | Min Disks | Fault Tolerance | Efficiency | Best For |
|---|---|---|---|---|
| RAID 0 | 2 | None | 100% | Speed, scratch data |
| RAID 1 | 2 | 1 disk | 50% | OS drives, critical data |
| RAID 5 | 3 | 1 disk | (N-1)/N | File servers, general use |
| RAID 6 | 4 | 2 disks | (N-2)/N | Large arrays, archives |
| RAID 10 | 4 (even) | 1 per mirror | 50% | Databases, high I/O |
Frequently Asked Questions
Is RAID a backup?
No. RAID protects against disk failure but does not replace backups. RAID cannot protect against accidental deletion, ransomware, fire, theft, or controller failure that corrupts all drives simultaneously. Always maintain separate backups using the 3-2-1 rule: 3 copies, 2 different media types, 1 offsite.
Which RAID level should I choose?
For personal NAS with 2 drives: RAID 1. For a small business file server with 3-4 drives: RAID 5. For large arrays or mission-critical data: RAID 6 or RAID 10. For temporary data where speed matters and loss is acceptable: RAID 0. Avoid RAID 5 with very large drives (8TB+) due to long rebuild times and URE risk.
Can I mix different disk sizes in RAID?
Traditional RAID uses the size of the smallest disk for all calculations, wasting capacity on larger drives. For example, mixing 2TB and 4TB drives in RAID 5 treats all as 2TB. Some systems like Synology SHR or UnRAID allow mixed sizes with better efficiency, but standard hardware RAID requires identical drives.