The most important key performance indicator (KPI) to monitor the effectiveness of disaster recovery processes is the percentage of IT systems meeting the recovery time objective (RTO) during the disaster recovery test. The RTO is the maximum acceptable time that a system orprocess can be unavailable after a disruption. The disaster recovery test is a simulation of a disaster scenario to evaluate the readiness and capability of the organization to restore its critical functions and systems. By measuring the percentage ofIT systems meeting the RTO during the test, the organization can assess how well the disaster recovery processes meet the predefined objectives and standards. Percentage of IT systems recovered within the mean time to restore (MTTR), percentage of issues arising from the disaster recovery test resolved on time, and percentage of IT systems included in the disaster recovery test scope are other possible KPIs, but they are not as important as the percentage of IT systems meeting the RTO. References = ISACA Certified in Risk and Information Systems Control (CRISC) Certification Exam Question and Answers, question 12; CRISC Review Manual, 6th Edition, page 215.