Reboot Window Plan Calculator

Work out reboot window plan instantly with clear inputs, formula shown and shareable results.

About Reboot Window Plan Calculator

Fitting a fleet into a maintenance window requires enough parallelism that hosts times per-host time divides into the window. Five hundred hosts at eight minutes each is 4,000 host-minutes, needing seventeen in parallel to fit four hours — which is only feasible with automation, since no small team supervises seventeen concurrent reboots manually.

Formula

Window planning

required parallelism = ceil(hosts x minutes per host / window minutes); hosts per window = window minutes x parallelism / minutes per host

Worked example

With the default values below, Reboot Window Plan Calculator returns Hosts to reboot in parallel of 17. Change any input above and every figure here is recalculated in your browser.

Inputs used

Hosts in scopeminimum 1: 500
Maintenance window lengthaccepts 0.1–24 h: 4 h
Minutes per host including verificationminimum 0.1 min: 8 min
Engineers supervisingminimum 1: 3

Results

Hosts to reboot in parallel: 17
Hosts completed per window: 510
Maintenance windows needed: 1
Parallel hosts per supervising engineer: 5.7

Step by step

1Values used
2Window planning
3Hosts to reboot in parallel= 17
4Hosts completed per window= 510
5Maintenance windows needed= 1
6Parallel hosts per supervising engineer= 5.7

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What if the required parallelism exceeds available redundancy?

Then the work needs more windows rather than more parallelism. Spreading across several nights is safer than taking too much capacity offline at once.

Can this be fully automated?

Yes, and it should be. Automated health checks between batches with an abort on failure is both faster and safer than manual supervision at this scale.