Domain 3 of 5 · Chapter 4 of 5

Resilience and Recovery

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Included in this chapter:

  • High availability, sites, diversity, and dispersion
  • Backups, replication, journaling, and power
  • COOP, capacity planning, testing, and the RTO/RPO model

Recovery site tiers vs cost, RTO, and readiness

AttributeHot siteWarm siteCold site
Equipment + dataFully provisioned, live data via replicationHardware in place, data periodically synced/staleSpace, power, connectivity only; no kit or data
Typical RTO (downtime)Seconds to minutes (near-instant failover)Hours to a day (configure + load recent data)Days to weeks (procure, install, restore)
RPO (data loss) achievableNear-zero with synchronous replicationHours (last sync interval)As old as last offsite backup
Relative costHighest (duplicate running environment)ModerateLowest
Best fitMission-critical, near-zero RTO/RPOImportant systems tolerating short outageNon-critical systems, long RTO tolerance

Decision tree

Threat = data corruption / ransomware (not site loss)? Yes Immutable / offline offsite backup or snapshot (NOT replication) No Downtime tolerance (RTO)? how fast must service return Near-zero (seconds) Hot / mirrored site + active/active cluster (highest cost) Hours Warm site hardware ready, load recent data Days Cold site (cheapest) restore from offsite backup Data-loss tolerance (RPO)? how much data may be lost Near-zero Synchronous replication + journaling (roll forward) Hours Scheduled backups frequency sets the RPO Always: geographically disperse the alternate site, encrypt backups, and test the plan (tabletop / parallel) before failover
Cheat sheet

Cheat sheet

  • RTO is downtime tolerance, RPO is data-loss tolerance
  • RTO must normally be shorter than MTD
  • Shorter RTO costs more
  • Hot, warm, and cold sites trade cost for readiness
  • Geographic dispersion defeats regional disasters
  • Load balancing scales; clustering fails over
  • High availability is not a backup
  • Platform diversity reduces correlated failure
  • Multi-cloud limits vendor and outage dependence
  • Backup frequency sets the RPO
  • Offsite backups survive site loss; encrypt them
  • Snapshots are point-in-time rollback, not offsite backups
  • Replication is not a backup
  • Journaling rolls forward to a precise point
  • An untested backup is just an assumption
  • UPS bridges; the generator sustains
  • A tabletop exercise is discussion-only
  • Parallel processing tests recovery without cutover
  • COOP keeps essential functions running
  • Capacity planning sizes people, technology, and infrastructure
  • MTBF measures reliability, MTTR measures repair speed
  • High availability defends the availability leg of CIA

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Also tested in

References

  1. CompTIA Security+ (SY0-701) Certification: Exam Objectives
  2. NIST SP 800-34 Rev. 1: Contingency Planning Guide for Federal Information Systems