4Service continuity & availability

• 4.1IT service continuity management (ITSCM), BCP, and disaster recovery

  Covers IT service continuity management (ITSCM), which restores a service within a target time after a major disruption such as a disaster; its relationship to the BCP (the business-wide continuity plan); the numeric recovery objectives RTO (recovery time objective), RPO (recovery point objective), and MTPD (maximum tolerable period of disruption); and the choice of recovery site among hot, warm, and cold sites, building judgment for selecting a continuity approach under constraints of business impact and cost.

• 4.2Availability management (availability rate, redundancy, single point of failure)

  Covers the availability rate, computed as MTBF / (MTBF + MTTR); the distinction between the mean time between failures (reliability, MTBF) and the mean time to repair (maintainability, MTTR); estimating overall availability as the product of availabilities for a series configuration and as 1 - (1 - a)^n for parallel redundancy; and eliminating a single point of failure (SPOF) through redundancy.

• 4.3Capacity management (demand forecasting, thresholds, trend analysis)

  Covers capacity management and its three sub-processes (business capacity management, service capacity management, and component capacity management), which secure exactly the performance and volume a service needs; demand management, which levels demand itself; early detection via threshold monitoring and trend analysis; and identifying the bottleneck, building judgment for choosing between augmentation and demand suppression.

• 4.4Backup and recovery (methods, RTO/RPO)

  Covers the differences and recovery procedures among full backup, incremental backup, and differential backup; generation management that retains multiple generations; off-site storage as protection against disaster; and how backup methods correspond to the recovery objectives (RTO, RPO), building judgment for selecting a method from business requirements.