NAS Capacity and RAID Planner

Usable TB and TiB, safety margin, hot spares, rebuild time and multi-vdev pools, with every formula tested. What you get: Excel planner (example + blank) for RAID 0, 1, 5, 6, 10 and RAIDZ1-3 with minimum-drive checks, TB to TiB,...

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Formats: Excel (.xlsx), Python script

What you can check before you buy

v1.0version · file dated Oct 14, 2026

2visible sheets in the workbook

45formulas, all readable in the cells

0formula error cells after a full recalculation

nonemacros in the spreadsheet file

Checked on Oct 14, 2026: the workbook nas-raid-capacity-planner-BLANK.xlsx was opened and fully recalculated in LibreOffice and no cell showed an error. This is our own check against the sold file, not an outside audit. The template was drafted with AI assistance; its formulas are checked with automated tests and worked examples.

Also included: raid_calc.py (a plain Python script you can read before running; no spreadsheet macros).

Inside the workbook (from the real file)

input cellformula (hover for the formula)heading

Sheet: Start_here (12 rows, 7 columns)

NAS Capacity + RAID Planner
Enter how many drives and their si
Formulas (n = drives that hold dat
TB vs TiB: a drive's '1 TB' is 10^
Hot spares are drives that hold no
The 'after margin' column subtract
Rebuild time is the best-case time
The 'Multi-vdev' block handles ZFS
Colour key: yellow = you type her
Created with AI assistance and rev

Sheet: Calc (29 rows, 8 columns)

Capacity calculator
Total drives installed
Drive size (TB, decimal as labelle
Filesystem overhead (%)
Free-space target (%)
Rebuild write speed (MB/s)
Hot spares (drives)
Drives in the array (n)
Best-case rebuild time (hours)
Level	Min drives	Check	Usable (TB)	Usable (TiB)	After margin (TiB)	Efficiency

Preview shows the first rows of each sheet as calculated. Your copy has the full sheets.

What is in the download

README.md

SOURCES.md

nas-raid-capacity-planner-BLANK.xlsx

nas-raid-capacity-planner-EXAMPLE.xlsx

raid_calc.py

Who it is for

Anyone choosing drives and a RAID or ZFS layout for a NAS or file server and wanting to know usable space before buying.
People comparing RAID 0, 1, 5, 6, 10 and RAIDZ1-3, with minimum-drive checks for each layout.
Planners who need to account for hot spares, a safety margin, filesystem overhead, a free-space target, TB to TiB conversion, best-case rebuild time and multi-vdev pools.

Who it is not for

Not a reliability simulator: it does not model how likely a pool is to fail.
Not a backup plan. Redundancy is not backup, and this tool does not replace one.
Vendor features such as hybrid RAID are not modelled, so owners relying on those should check the vendor's own figures.

About this template

Usable TB and TiB, safety margin, hot spares, rebuild time and multi-vdev pools, with every formula tested.

What you get: Excel planner (example + blank) for RAID 0, 1, 5, 6, 10 and RAIDZ1-3 with minimum-drive checks, TB to TiB, filesystem overhead and free-space target, hot spares, best-case rebuild time and multi-vdev pools; Python CLI; 16 workbook tests + 14 script tests.

Who it is for: Anyone choosing drives and a layout for a NAS or file server.

Files:

`nas-raid-capacity-planner-BLANK.xlsx`
`nas-raid-capacity-planner-EXAMPLE.xlsx`
`raid_calc.py`

How to use: open the EXAMPLE file first to see every formula working (yellow cells = your inputs, blue-grey = formulas); then use the BLANK file for your own data. See Start_here sheet / included notes. Test examples are in the Tests sheet or `--selftest` where included.

What it is NOT: Not a reliability simulator and not a backup plan: redundancy is not backup. Vendor features such as hybrid RAID are not modelled.

Questions

What file types do I get?

Two Excel workbooks (.xlsx), one example and one blank, plus a Python script (raid_calc.py) that runs as a command-line tool. README.md and SOURCES.md are also included.

Can I edit the formulas?

The workbooks contain 45 formulas across 2 sheets. Yellow cells are your inputs and blue-grey cells are formulas. The EXAMPLE file shows each formula working, and the BLANK file is for your own data.

How do I start, and does it replace an engineer?

Open the EXAMPLE file first, then move to the BLANK file with your own drive sizes and layout. It is a planning tool for estimating capacity, not a replacement for professional design advice or a backup strategy.

Refunds: refunds follow the rules of the marketplace where you buy; if a file is broken we fix or replace it (details). It is a planning tool, not tax, legal, financial or engineering advice. Check rates, limits and rules against the official source before you rely on them. How we check our files.