RAID Calculator

Calculate usable RAID capacity, parity overhead, and fault tolerance for RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10 arrays. Estimate storage efficiency and redundancy for NAS, server, and CCTV NVR deployments.
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RAID Setups2
Setup 1
Unit
TB
Unit
Setup 2
Unit
TB
Unit
Calculation Result
SetupRAID LevelDrivesRaw CapacityUsable CapacityOverheadFault ToleranceStatus
4x 4TB RAID 5RAID 5 (Striped Parity)416.00 TB12.00 TB25.0%1 drive(s)Configuration Valid
8x 4TB RAID 6BestRAID 6 (Double Parity)8 (+1 spare)32.00 TB24.00 TB25.0%2 drive(s)Configuration Valid
Capacity Comparison
4x 4TB RAID 5: Configuration Valid8x 4TB RAID 6: Configuration Valid

2 of 2 configuration(s) are valid. 8x 4TB RAID 6 provides the most usable capacity at 24.00 TB.

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Overview

The RAID Calculator estimates usable capacity, parity overhead, redundancy, and fault tolerance for RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10 arrays. Compare multiple setups side by side in a table and capacity chart to choose the right RAID level and drive count for your storage and reliability needs across NAS, servers, and CCTV NVR deployments.

Common Use Cases

How to Use

1
Click Add Setup to create as many configurations as you want to compare.
2
Give each setup a name so it is easy to tell apart in the comparison table and chart.
3
For each setup, select the RAID level you want to evaluate.
4
Enter the total number of drives in the array, the size of a single drive in terabytes, and how many hot spare drives are reserved.
5
Review the comparison table for raw capacity, usable capacity, capacity overhead, and fault tolerance side by side.
6
Read the grouped bar chart to visually compare raw versus usable capacity across all setups.

Example Scenario

Four-Drive NAS with RAID 5

A small office builds a 4-bay NAS using four 4 TB drives. With RAID 5 the usable capacity is 12 TB (one drive of parity), and the array tolerates a single drive failure without data loss.

Technical Notes

RAID 0 stripes data across all drives with no parity. It offers maximum capacity and performance but provides zero redundancy, so any single drive failure loses the whole array.

RAID 1 mirrors data across all drives. Usable capacity equals the size of a single drive, and all but one drive can fail without losing data.

RAID 5 stripes data with distributed parity across the array. It loses one drive of capacity to parity and tolerates a single drive failure.

RAID 6 uses two parity blocks across the array. It loses two drives of capacity and tolerates two simultaneous drive failures.

RAID 10 mirrors pairs of drives and stripes across the pairs. It combines speed with redundancy but uses half the raw capacity, and each mirror pair tolerates one failure.

A hot spare is a standby drive that automatically replaces a failed drive in the array. It is reserved for replacement and does not add usable capacity.

Capacity overhead is the portion of raw capacity consumed by parity or mirroring. Lower overhead means more usable storage but usually less redundancy.

Fault tolerance indicates how many drives can fail at the same time before data loss occurs.

Common Mistakes

Frequently Asked Questions

RAID 0 for speed with no redundancy, RAID 1 for mirrored safety, RAID 5 as a balanced choice for 3 or more drives, RAID 6 for stronger protection with 4 or more drives, and RAID 10 when performance and redundancy both matter.

RAID 5 provides N minus 1 drives of usable capacity, where N is the number of drives. For example, four 4 TB drives give 12 TB usable.

Many RAID controllers limit the array to the size of the smallest drive. Matching drive sizes is recommended to avoid wasted capacity.

A hot spare is a drive that stays idle in the system and automatically replaces a failed drive, helping the array rebuild itself without waiting for a human to swap hardware.

RAID protects against drive failure, not against deletion, corruption, theft, or disasters. Always keep an independent backup in addition to RAID.

Related Topics

RAID levelsNAS storageData redundancyServer storageCCTV storage planningBackup strategyDisk fault toleranceStorage capacity planningHot spare configurationHard drive sizing