Which of the following is the BEST concept to maintain required but non-critical server availability?

SaaS site is not a standard disaster recovery site classification; SaaS refers to a cloud software delivery model, not a business continuity facility type.

A cold site provides only physical space and basic utilities with no pre-installed hardware, resulting in the longest recovery time, making it unsuitable for maintaining availability.

A hot site mirrors the production environment in real time and enables near-instant failover, which is excessive and cost-prohibitive for non-critical servers.

A warm site is a recovery facility that has hardware and connectivity pre-installed but requires some configuration and data restoration before becoming fully operational. It is the best fit for required but non-critical servers because it offers faster recovery than a cold site at a lower cost than a hot site. This balance of availability and expense is appropriate when the servers are needed but do not require immediate failover.