Backup, Disaster Recovery and Business Continuity
Domain 7 tests the definitions of RPO and RTO, backup design rules, and the difference between a disaster recovery plan and a business continuity plan. Calculation items give a schedule and a failure time and ask for the data loss window.
Definitions and strategy
RPO is the maximum tolerable data loss, measured backwards from the failure. RTO is the maximum tolerable time to restore service. Both come from a business impact analysis, not from IT preference. The 3-2-1 rule: three copies, on two media types, one offsite. Add an offline or immutable copy so ransomware cannot encrypt the backup set, encrypt backups in transit and at rest, and separate retention (operational recovery) from archive (long-term legal hold).
DR and BC
DR tiers: cold site (space and power only, longest RTO), warm site (partial equipment, restore from backup), hot site (near-real-time, shortest RTO). Active-active gives continuous service; active-passive relies on failover. The DR plan is the technical recovery runbook; the BC plan covers business processes, staff, suppliers and communications. Exercise the plans as tabletop, walkthrough and full failover drills, and update them after every real incident or major change.
Worked example
Nightly full backup at 01:00 plus hourly log backups; the array fails at 10:20; measured restore time is 3 hours; the business requires RTO of 1 hour and RPO of 30 minutes. Current RPO is about 20 minutes (logs to 10:00), which passes; RTO of 3 hours fails the target. Options: a standby server with log shipping applied every 10 minutes, faster restore storage, or an automated runbook. Reasoning: RPO and RTO are independent constraints, and the schedule is only acceptable if both are met.
Traps
- Swapping RTO and RPO in the answer.
- Claiming RAID, snapshots or replication are backups; they propagate deletions and encryption.
- Treating an untested backup as a valid backup.
- Keeping the only copy in the same room or on the same domain.
- Deleting retention sets that are subject to a legal hold.