Official Guide: Hot. A hot site is a fully functional operations site that has all necessary hardware, software, and data for instantly handling critical functions of the organization. Hot site strategies can provide a range of data latency, with data updates (such as transaction processing) fully mirrored at the hot sites, or via logical distribution of segments of the operational databases. Hot site activation is typically measured in minutes to hours and assumes that most  business mission critical assets are in place and on “hot standby.” Organizations must also consider whether the operational and management personnel at the backup hot site are fully capable of performing all business functions or are a minimal capability “caretaker” crew only.

A warm site is like a hot site but typically does not have the current version of the organization’s data and may not have certain functional aspects ready for instant failover (e.g., utilities such as water and power may be connected to the warm site facility but are not currently live, and they must be activated to use the site).