Chapter 3 - section 3.3 - explain disaster recovery (DR) concepts.

Objective – Disaster Recovery and High Availability

• DR metrics
▸ Recovery point objective (RPO)
▸ Recovery time objective (RTO)
▸ Mean time to repair (MTTR)
▸ Mean time between failures (MTBF)
• DR sites
▸ Cold site
▸ Warm site
▸ Hot site
• High-availability approaches
▸ Active-active
▸ Active-passive
• Testing
▸ Tabletop exercises
▸ Validation tests

DR Metric – Recovery Point Objective (RPO)

• Maximum acceptable amount of data loss
• Measured in time (minutes or hours)
• Determined by backup frequency
• Focuses on data loss tolerance (exam critical)

DR Metric – Recovery Time Objective (RTO)

• Maximum acceptable downtime
• Time required to restore service after failure
• Lower RTO requires higher cost
• Focuses on service availability

DR Metric – Mean Time to Repair (MTTR)

• Average time required to repair a failed system
• Includes diagnosis, repair, and restore
• Lower MTTR improves availability
• Used in availability calculations

DR Metric – Mean Time Between Failures (MTBF)

• Average operational time between failures
• Measures system reliability
• Higher MTBF means fewer failures
• Commonly paired with MTTR

DR Site – Cold Site

• Basic facility only
• No active hardware or data
• Requires full restoration
• Longest recovery time
• Lowest cost

DR Site – Warm Site

• Partial infrastructure available
• Some hardware and data present
• Moderate recovery time
• Moderate cost

DR Site – Hot Site

• Fully operational duplicate environment
• Real-time or near-real-time data replication
• Fastest recovery time
• Highest cost

High Availability – Active-Active

• All nodes actively handle traffic
• Load is shared across systems
• No downtime during failure
• Complex design and higher cost

High Availability – Active-Passive

• One system active, one on standby
• Passive system activates on failure
• Simpler design than active-active
• Brief failover delay possible

DR Testing – Tabletop Exercises

• Discussion-based walkthrough
• No production systems impacted
• Validates procedures and roles
• Low cost and low risk

DR Testing – Validation Tests

• Simulates actual disaster recovery
• Systems are failed over and restored
• Confirms recovery objectives are met
• Higher risk but most accurate

N10-009 Sample Questions – Disaster Recovery

• Q: Which metric defines acceptable data loss?
▸ A: Recovery Point Objective (RPO)
• Q: Which DR site provides the fastest recovery?
▸ A: Hot site
• Q: Which HA model allows all nodes to process traffic?
▸ A: Active-active
• Q: Which test validates real recovery capability?
▸ A: Validation test