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RAID Capacity Calculator

Select your RAID level, number of disks and disk size. Get usable capacity, redundancy overhead, fault tolerance and an honest risk verdict — instantly, no login.

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●100% client-side
●RAID 0/1/5/6/10/JBOD
Configure your RAID array
224
3 × 4 TB = 12 TB raw total

Fault tolerance

1

disk can fail

Data risk — Moderate safety

3 × 4 TB RAID 5

Distributed parity — 1 disk fault tolerance, good efficiency

Usable capacity

8 TB

Redundancy overhead

4 TB

Efficiency

67%

Storage efficiency67%

RAID is not a backup

Even a RAID 6 array can be wiped out by ransomware, accidental deletion, controller failure, a fire, or a user error. RAID protects against hardware failure only — it is not a substitute for an off-site backup.

RAID data recovery guideRecover from failed RAID with EaseUS
Best data recovery softwareRAID data recovery — complete guide
How it works

RAID capacity formulas explained

This calculator applies the standard RAID capacity formulas used by storage engineers. All computation is client-side — no data is sent to any server. Choose your RAID level, adjust disk count and size, and results update in real time.

Usable vs raw

Raw capacity is n disks times their size. Usable capacity subtracts parity and mirror overhead. Only usable space can store your data.

Fault tolerance

Fault tolerance is the number of drives that can die without data loss. RAID 5 = 1. RAID 6 = 2. RAID 10 = 1 guaranteed (often more). RAID 0 = 0.

RAID vs backup

RAID protects against disk hardware failure only. Ransomware, accidental deletion and controller failure bypass all RAID redundancy. Always maintain an offline backup.

RAID is not a backup — understand the limits

RAID is a hardware availability mechanism, not a data protection strategy. These scenarios will destroy your data regardless of RAID level:

  • ⚠

    Ransomware encrypts all connected volumes in real time — RAID 6 included.

  • ⚠

    Accidental deletion or overwrites replicate instantly across all mirrors.

  • ⚠

    RAID controller failure can make the entire array unreadable without the original controller firmware.

  • ⚠

    Fire, flooding or theft removes all physical disks simultaneously.

  • ⚠

    Silent data corruption (bit rot) on aging drives can propagate before parity catches it on RAID 5.

If your RAID already failed

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Related guides

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RAID data recovery — complete guide

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Best data recovery software — 8-tool benchmark

Frequently asked questions

How is usable RAID capacity calculated?
RAID 0 and JBOD use 100% of raw space (n disks). RAID 1 uses only 1 disk worth of space regardless of count. RAID 5 uses (n-1) disks. RAID 6 uses (n-2) disks. RAID 10 uses n/2 disks. This calculator applies those exact formulas client-side.
What is RAID fault tolerance?
Fault tolerance is the number of drives that can fail simultaneously without data loss. RAID 0 and JBOD tolerate zero failures. RAID 1 tolerates n-1 failures (all but one mirror). RAID 5 tolerates exactly 1 failure. RAID 6 tolerates 2. RAID 10 tolerates at least 1 (one per mirror pair).
Is RAID 5 still safe in 2026?
RAID 5 is risky with large drives (8 TB+) because rebuild times can exceed 24 hours. During a rebuild, a second drive failure causes total data loss. For large arrays, RAID 6 (2-disk fault tolerance) or ZFS RAIDZ2 is strongly recommended.
Can I recover data from a failed RAID array?
Yes, in many cases. Software like EaseUS can reconstruct RAID 5 and RAID 6 volumes if you still have enough healthy disks (n-1 for RAID 5, n-2 for RAID 6). For physically damaged disks or controller failures, a professional lab is required.
Why does RAID 10 need an even number of disks?
RAID 10 mirrors pairs of disks, then stripes across those pairs. An odd number of disks cannot form complete mirror pairs. Minimum is 4 disks (2 mirrored pairs).

Save My Disk may earn a commission via Commission Junction if you purchase EaseUS through our links (same price for you). This does not affect our recommendations — reproducible methodology with Zenodo study DOI 10.5281/zenodo.20507434.