What is the minimum drive count for each RAID level?

RAID 0 and RAID 1 need at least 2 drives. RAID 5 needs at least 3. RAID 6 needs at least 4. RAID 10 needs at least 4 (and must be an even number).

How does RAID 5 calculate usable space?

RAID 5 dedicates the equivalent of one drive's capacity to parity data, spread across all drives. Usable space = (N - 1) × drive size, where N is the number of drives.

What is the difference between RAID 6 and RAID 5?

RAID 6 uses double distributed parity, tolerating up to 2 simultaneous drive failures instead of 1. Usable space = (N - 2) × drive size, costing one extra drive's worth of capacity compared to RAID 5.

Does RAID replace backups?

No. RAID protects against drive hardware failure but does not protect against accidental deletion, ransomware, file corruption, or controller failure. Always maintain separate backups.

Why does RAID 10 require an even number of drives?

RAID 10 mirrors drives in pairs (RAID 1) and then stripes across those pairs (RAID 0). Each pair needs exactly 2 drives, so the total must be even.

What does storage efficiency mean here?

Efficiency is the percentage of raw total capacity that is available for storing data. RAID 0 is 100% efficient (no redundancy). RAID 1 with 2 drives is 50% efficient. Higher efficiency means more usable space per dollar spent on drives.

RAID Capacity Calculator

Name: RAID Capacity Calculator
Availability: InStock
Author: Nham Vu

Enter the number of drives and drive size to instantly see usable capacity, overhead, and fault tolerance for RAID 0, 1, 5, 6, and 10.

Array Configuration

Number of drives

Minimum: 2 drives

Drive capacity

Total raw capacity 16 TB

Drives entered 4

RAID Level Comparison

Levels that require more drives than configured are grayed out.

RAID Level	Usable Space	Overhead	Efficiency	Drives can fail

Summary

Enter the number of drives and drive size to instantly see usable capacity, overhead, and fault tolerance for RAID 0, 1, 5, 6, and 10.

How it works

Enter the number of drives in your array.
Enter the capacity of each individual drive.
Select the unit (GB or TB).
All supported RAID levels update instantly with usable capacity and overhead.
Check the fault tolerance column to see how many drives can fail before data loss.
Use the efficiency row to compare how much raw storage each RAID level actually uses for data.

Use cases

Plan NAS or server storage before purchasing drives.
Compare RAID levels to balance capacity versus redundancy for a budget.
Verify usable space estimates from a hosting provider or storage vendor.
Determine the minimum drive count needed for RAID 5 or RAID 6.
Teach or study RAID concepts in a computer science or IT course.
Evaluate whether to add a drive to increase capacity or fault tolerance.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu