RAID 0, 1, 5, 6, 10 Explained Simply

What Is RAID?

RAID stands for Redundant Array of Independent Disks. It's a way to combine multiple hard drives to either increase speed, add backup protection, or both. Each RAID level makes different tradeoffs. Use our RAID calculator to model exact usable storage and cost for your setup.

RAID 0: Speed, No Protection

Usable Capacity: 100% of total (4 drives × 4TB = 16TB)

Fault Tolerance: None — one drive fails = all data lost

RAID 0 stripes data across drives for maximum speed. It's only suitable for cache/temporary data. Never use for irreplaceable files.

RAID 1: Mirroring

Usable Capacity: 50% of total (2 drives × 4TB = 4TB)

Fault Tolerance: One drive can fail

RAID 1 duplicates data across two drives. Fast reads, but half the capacity. Good for small 2-bay NAS systems.

RAID 5: Balanced Protection

Usable Capacity: 75% of total (4 drives × 4TB = 12TB)

Fault Tolerance: One drive can fail

RAID 5 uses parity to protect against one drive failure while using less space than RAID 1. The most common choice for 3-5 drive NAS systems. Always use CMR drives — SMR drives can stall during RAID 5 rebuilds and cause data loss.

RAID 6: Extra Protection

Usable Capacity: 50% of total (4 drives × 4TB = 8TB)

Fault Tolerance: Two drives can fail

RAID 6 is like RAID 5 but with two layers of parity. Recommended for 4+ drive systems. Slower writes than RAID 5, but much safer during rebuilds.

RAID 10: Speed + Protection

Usable Capacity: 50% of total (4 drives × 4TB = 8TB)

Fault Tolerance: Up to two drives can fail

RAID 10 mirrors drives and stripes them together. Faster than RAID 5/6 but requires at least 4 drives (minimum). Great for performance-critical setups.

Which RAID Is Right for You?

2 Drives

Use RAID 1 (mirroring)

3 Drives

Use RAID 5

4 Drives

Use RAID 6 (recommended) or RAID 10 for speed

5+ Drives

Use RAID 6 for safety, or RAID 10 if you need performance