About

When configuring a server or Network Attached Storage (NAS), choosing the right RAID (Redundant Array of Independent Disks) level is the most critical decision a system administrator makes. It is a tradeoff between three factors: performance (speed), redundancy (safety), and capacity (space).

This RAID Calculator simplifies this complexity. By selecting your drive count and size, it visualizes exactly how much raw storage you are buying versus how much you can actually use for data. It calculates the 'RAID Penalty'—the space lost to parity or mirroring—and informs you of the fault tolerance (how many drives can fail before data loss occurs).

Formulas

Capacity calculations depend on n (number of drives) and s (size of smallest drive).

Cap_RAID5 = (n − 1) × s

Cap_RAID6 = (n − 2) × s

Cap_RAID10 = (n / 2) × s

Reference Data

RAID Level	Min Drives	Fault Tolerance	Read Speed	Write Speed	Capacity Efficiency
RAID 0	2	0 (None)	Very High (nX)	Very High (nX)	100%
RAID 1	2	1 Drive	High (nX)	Medium (1X)	50%
RAID 5	3	1 Drive	High ((n-1)X)	Medium (Slow Parity)	67% - 94%
RAID 6	4	2 Drives	High ((n-2)X)	Slow (Double Parity)	50% - 88%
RAID 10	4	Up to n/2	Very High (nX)	High (n/2 X)	50%

Frequently Asked Questions

Hard drive manufacturers define 1 TB as 1,000,000,000,000 bytes (decimal), while operating systems often calculate 1 TB as 1,099,511,627,776 bytes (binary/TiB). Additionally, formatting (file system overhead) typically consumes another 2-5% of space.

RAID is NOT a backup. RAID provides redundancy (uptime). If a file is corrupted or deleted, it is corrupted on the mirror too. For backup storage servers, RAID 6 is often preferred for its dual-disk failure protection during long rebuild times.

Yes, but in standard RAID configurations, the array is limited by the smallest drive. If you mix a 4TB and an 8TB drive in RAID 1, you will only have 4TB usable. The remaining 4TB on the larger drive is wasted.