Industrial Cybersecurity & OT Risk calculator

Cyber Recovery Spares Buffer Calculator

The Cyber Recovery Spares Buffer sizes the inventory of clean spare hardware — servers, switches, HMIs, drives and known-good controllers — you need on hand to rebuild OT systems after a destructive cyber incident such as ransomware or wiperware. It combines cycle stock (daily recovery demand times replenishment lead time) with a safety-stock buffer for demand and lead-time variability. OT resilience and business-continuity planners use it because, in a real incident, supply chains for industrial hardware can stretch to weeks and you cannot wait for a vendor RMA while a plant is down. It translates an abstract recovery-time objective into a concrete number of physical spares to stage.

What this calculator does

  • Estimate required recovery spares inventory for cyber recovery using daily demand, replenishment lead time, and safety stock.
  • Use it when sizing spare HMIs, industrial PCs, network gear, storage media, and recovery kits for OT resilience.
  • It computes the required recovery-spares inventory as cycle stock (daily demand times lead time) plus a safety-stock buffer.

Formula used

  • Cyber recovery spares cycle stock = daily recovery spares demand × recovery spares replenishment lead time
  • Required cyber recovery spares inventory = cycle stock + recovery spares safety stock

Inputs explained

  • Daily recovery spares consumption rate:
  • Recovery spares replenishment lead time:
  • Recovery spares safety stock held:

How to use the result

  • Use it when building a cyber-recovery plan or incident-response runbook that depends on rapidly reimaging or replacing compromised OT hardware.
  • It assumes steady daily demand and a known lead time; a large simultaneous-loss event (every HMI on a line wiped at once) is a spike this cycle-stock model doesn't capture and should be planned for separately.

Common questions

  • How do you size a cyber recovery spares buffer? Multiply daily recovery spares demand by the replenishment lead time to get cycle stock, then add your safety stock. With 2 units/day and 21 days lead time you need 42 units of cycle stock, plus a 12-unit buffer.
  • Why hold dedicated cyber recovery spares at all? After a destructive attack you may need to rebuild many systems from clean hardware before re-trusting anything on the network. Industrial hardware lead times of weeks mean ordering reactively can extend downtime well past your recovery-time objective.
  • How much safety stock should recovery spares carry? Enough to cover variability in both demand and lead time. The longer and less reliable your supplier lead time, the larger the buffer — many OT teams hold weeks of cover for long-lead controllers and switches.
  • What lead time should I use? Use the realistic replenishment time under stressed conditions, not the catalog figure. The 21-day default reflects how long genuinely clean, validated industrial hardware can take to arrive during a supply crunch.
  • Should clean OS images count as recovery spares? The hardware count is what this buffer sizes, but every physical spare is only useful with a tested, offline gold image ready to deploy. Pair the spares buffer with a validated image library and restore runbook.

Last reviewed 2026-05-12.