RTO and RPO
Stands forRecovery Time Objective / Recovery Point Objective
How long a system may be down, and how much data may be lost. The two objectives that decide how long a maintenance window you can afford.
Also calledRTO · RPO · recovery objectives
RTO — how long may pass before the service is back. RPO — how much data may be lost, that is, how far back you may restore to.
Both come from disaster recovery, but they bear directly on maintenance windows: the recovery time objective is in effect the window's budget. A system permitted one hour of downtime will not get a four-hour window, so its update has to be staged differently, or rolled across nodes.
The recovery point objective decides something else: when the backup has to be taken before you start, and what the checklist must verify before installation begins.