CalculatorShelf
MethodologyVisible assumptions
Storage · Interactive calculator

Mixed Drive RAID Calculator

See how mixed drive sizes can waste capacity when an array is limited by the smallest disk.

Interactive calculatorFormula shownVisible assumptions
Updated 2026-06-24
Calculation method MIXED_DRIVE_RAID-1.0
Page type Interactive calculator
Tool type Formula shown

Calculate mixed-drive RAID waste

Estimate what happens when a RAID array contains different drive sizes. Generic RAID usually treats each disk as if it were the size of the smallest disk, leaving extra space unused.

Primary result

Usable capacity 24 TB
Installed raw 38 TB
Wasted by smallest-drive rule 6 TB
Smallest drive 8 TB
Efficiency vs installed 63.2%
Fault tolerance 1 drive

The generic RAID estimate uses the 8 TB smallest drive as the effective size for each disk.

Generic RAID usually sizes each disk as if it were the smallest drive. Vendor hybrid modes may differ.

Quick answer

If you combine 8 TB, 8 TB, 10 TB, and 12 TB drives in generic RAID 5, the array is calculated as four 8 TB drives. The extra 2 TB and 4 TB on the larger disks are typically wasted.

Best for: comparing realistic scenarios before acting. Not for: final professional guidance, emergency decisions, or replacing product labels and local requirements.

How to use the calculator

  1. Enter the labeled inputs for this mixed drive raid scenario.
  2. Adjust the optional assumptions shown in the form instead of relying on defaults blindly.
  3. Read the primary result, supporting result cards, and any warning notes together.
  4. Use share, copy, or print/PDF to save the exact scenario for later comparison.

What the results mean

The primary result is the main number to use first. Supporting cards show the inputs, ranges, assumptions, or follow-up checks that explain how to interpret it.

Decision notes for this calculator

How to interpret this calculator

The labeled inputs and visible assumptions drive the result.

Sources and assumptions

Use the inputs, units, and assumptions shown on the page, then compare important results with product documentation, vendor guidance, local code, or a qualified professional when the decision has safety or cost consequences.

Method version: MIXED_DRIVE_RAID-1.0. Send corrections through the contact page.

What to do next

Compare a conservative scenario with your real measurements before acting.

See how mixed drive sizes waste capacity

Mixed-drive RAID arrays are often limited by the smallest active disk. This calculator makes the wasted capacity visible so you can decide whether to reuse older drives, replace the smallest disk, or choose a different layout.

  • Inputs: individual drive sizes, RAID level, hot spares, and overhead assumptions.
  • Outputs: usable capacity, raw capacity, wasted capacity, parity or mirror reserve, and upgrade notes.
  • Compare: use the NAS capacity calculator for bay planning and the Disk RAID calculator for equal-drive scenarios.

Formula / methodology

Effective per-drive size = smallest drive size. Generic usable capacity = RAID formula using effective size. Wasted capacity = installed raw capacity − effective raw capacity.

Assumptions and limitations

  • Inputs are assumed to be measured accurately and entered in the units shown.
  • Rounding is intentional so the result is easier to use in real decisions.
  • Vendor-specific behavior, local code, product labels, and regional pricing can override a generic calculator.
  • Health, legal, tax, emergency, structural, chemical, and other high-risk decisions need qualified guidance beyond a web calculator.

Example calculation

Input: 8 TB, 8 TB, 10 TB, 12 TB in RAID 5. Output: installed raw 38 TB, effective raw 32 TB, usable about 24 TB, and about 6 TB wasted before overhead.

The worked example uses the same default scenario so the formula can be followed without running JavaScript.

Common mistakes

  • Expecting generic RAID to use every terabyte on larger disks.
  • Mixing vendor hybrid modes with generic RAID math.
  • Ignoring upgrade order when replacing small drives.
  • Comparing installed raw capacity to usable capacity without separating parity and wasted space.

FAQ

What formula does this page use?

Effective per-drive size = smallest drive size. Generic usable capacity = RAID formula using effective size. Wasted capacity = installed raw capacity − effective raw capacity.

What changes the result the most?

The smallest drive size drives the result most because generic RAID treats each disk as if it were that smallest member.

How should I use this result?

Use it as a planning estimate and compare important decisions with product documentation, labels, quotes, local code, or qualified guidance.

Why does this page show warnings?

Warnings call out assumptions that can materially change the result or create safety, cost, or reliability problems.

Can I share this scenario?

Yes. The share button copies a URL with the current inputs, while the main page remains the base calculator URL.

Method details

Updated: June 24, 2026. Calculation method: MIXED_DRIVE_RAID-1.0. Availability: interactive calculator.