RAID Calculator

Calculate usable capacity, raw capacity, storage efficiency, redundancy overhead, and fault tolerance based on RAID level, drive count, and drive capacity. RAID Calculator helps IT administrators, storage engineers, and home lab users plan reliable arrays and compare RAID configurations.

Highlights

  • Compare RAID 0, 1, 5, 6, and 10 configurations.
  • Calculate raw and usable storage capacity instantly.
  • Measure storage efficiency and redundancy overhead.
  • Estimate guaranteed disk failure protection.
  • Support arrays from 2 to 256 disks and capacities from MB to PB.

Table of Contents

  1. How RAID Calculator Works?
  2. Practical Use Cases
  3. Accuracy and Limitations
  4. Quick Examples
  5. Frequently Asked Questions (FAQs)
  6. Cite This Calculator

How RAID Calculator Works?

The RAID Calculator estimates array capacity and protection from three inputs: RAID level, number of disks, and capacity per disk. It assumes that all disks have the same usable capacity and applies the standard capacity model for each supported RAID architecture.

Raw Capacity=Number of Disks×Capacity per Disk

Raw capacity is the combined capacity of every disk before parity or mirroring is reserved. Usable capacity depends on the selected RAID level:


RAID levelUsable capacityCapacity efficiencyRedundancy overheadGuaranteed disk failures
RAID 0n×C100%00
RAID 1C1n×100%(n-1)×Cn-1
RAID 5(n-1)×Cn-1n×100%C1
RAID 6(n-2)×Cn-2n×100%2×C2
RAID 10n2×C50%n2×C1 guaranteed

Here, n represents the number of disks and C represents the capacity of one disk. Capacity efficiency is calculated as usable capacity divided by raw capacity.

Capacity Efficiency=Usable CapacityRaw Capacity×100%

Redundancy overhead is the capacity reserved for mirroring or parity rather than application data.

Redundancy Overhead=Raw Capacity-Usable Capacity

RAID 0 provides striping without redundancy. RAID 1 mirrors data, RAID 5 reserves the equivalent of one disk for distributed parity, RAID 6 reserves the equivalent of two disks, and RAID 10 combines mirroring with striping. RAID 5 normally requires at least three disks, RAID 6 at least four, and RAID 10 is normally built with an even number of at least four disks.

Practical Use Cases

IT administrators: Compare RAID 5, RAID 6, and RAID 10 when planning a file server or business storage array. The calculator shows how much raw capacity is lost to protection and whether the selected design can tolerate one or two disk failures.

Storage engineers: Evaluate capacity efficiency across different disk counts before designing a storage system. For example, increasing the number of disks can improve the efficiency of RAID 5 or RAID 6 while preserving the associated parity protection model.

Home lab users: Estimate the usable space available for virtual machines, backups, media, or containers. RAID 10 may be useful when performance and predictable mirroring are more important than maximizing usable capacity.

NAS owners: Compare the trade-off between usable storage and protection before populating a network-attached storage enclosure. The raw capacity, usable capacity, and redundancy overhead outputs make it easier to see how much space is reserved for RAID protection.

Backup and media administrators: Calculate whether an array has enough usable capacity for planned data growth while checking its guaranteed disk-failure tolerance. RAID protection improves availability, but it should not be treated as a substitute for an independent backup.

Accuracy and Limitations

The calculator is mathematically accurate for standard RAID capacity models using identical disks with the entered formatted capacity. It assumes RAID 1 uses one mirrored data copy, RAID 5 uses one disk-equivalent of parity, RAID 6 uses two disk-equivalents, and RAID 10 uses mirrored pairs. RAID 10 fault tolerance is reported conservatively as one guaranteed disk failure because additional failures can be tolerated only when they occur in different mirror pairs. The estimates do not include filesystem overhead, hot spares, reserved blocks, controller metadata, rebuild performance, degraded-array behavior, or usable capacity reductions imposed by a specific storage platform. RAID 0 has no fault tolerance, and RAID protection does not replace a separate backup.

Quick Examples

Example #1: Eight-Disk RAID 5

Estimate usable capacity and fault tolerance for a balanced RAID 5 storage array.

Example #2: Mirrored Home Lab Storage

Calculate the capacity and redundancy overhead of a four-disk RAID 10 array.

Example #3: High-Resilience RAID 6

Plan a large array designed to remain operational after two disk failures.

Frequently Asked Questions

Raw capacity is the combined size of all drives. Usable capacity is the storage available for data after accounting for mirroring or parity protection.

Protection depends on the RAID level: RAID 0 protects against none, RAID 1 and RAID 5 typically protect against one drive failure, RAID 6 protects against two, and RAID 10 can tolerate multiple failures depending on which drives fail.

RAID 0 generally provides the highest usable capacity because it has no redundancy. However, it offers no protection against drive failure.

For predictable results, drives should have matching capacities. When different-sized drives are used, the array may limit each drive to the capacity of the smallest one.

No. RAID helps maintain availability when drives fail, but it does not protect against accidental deletion, malware, hardware failure, theft, or other data-loss events.

Cite This Calculator