1. Redundancy Planning
   1. Redundant Power
      1. Undesirable Power Conditions
         1. Surge:
            1. An unexpected increase in the amount of voltage provided.
         2. Spike:
            1. A short transient in voltage that can be due to a short circuit, tripped circuit breaker, power outage, or lightning strike.
         3. Sag:
            1. An unexpected decrease in the amount of voltage provided.
         4. Brownout:
            1. When the voltage drops to such an extent that it typically causes the lights to dim and causes computers to shut off.
         5. Blackout:
            1. When a total loss of power for a prolonged period occurs.
      2. Redundant Power Supplies
         1. An enclosure that contains two complete power supplies, the second of which turns on when the first fails.
      3. Uninterruptible Power Supplies
         1. Takes the functionality of a surge suppressor and combines that with a battery backup, protecting computers not only from surges and spikes, but also from sags, brownouts, and blackouts.
      4. Generators
         1. Backup Generator:
            1. Part of an emergency power system used when there is an outage of regular electric grid power.
         2. Standby Generator:
            1. Systems that turn on automatically within seconds of a power outage.
   2. Redundant Data
      1. Disk Duplexing:
         1. When each disk is connected to a separate controller.
      2. RAID
   3. Redundant Networking
      1. Redundant ISP:
         1. Secondary connections to another ISP; for example, a backup T-1 line.
   4. Redundant Servers
      1. Cluster:
         1. Two or more servers that work with each other.
   5. Redundant Sites
      1. Hot Site
         1. Offsite backups that may replace the current active site in case of an adverse security incident
         2. Most expensive
      2. Cold Site
         1. Offsite backups in storage that cannot immediately be brought online in case of a security incident
         2. Least expensive
      3. Warm Site
         1. An offsite location containing the offline hardware that would be required to replace the current active site. Data needed to replace the current active site is not immediately available, but may be accessed.
         2. Middle ground in terms of cost
   6. Redundant People
      1. Separation of Duties
      2. Job Rotation
2. Failure and Recovery Concepts
   1. Single Point of Failure
      1. An element, object, or part of a system that, if it fails, will cause the whole system to fail.
   2. Mean Time Between Failures (MTBF)
      1. The average number of failures per million hours of operation for a product, based on historical baselines. It can be very helpful when making quantitative assessments.
   3. Mean Time to Repair (MTTR)
      1. The time needed to repair a failed device
   4. Mean Time to Failure (MTTF)
      1. A basic measure of reliability for devices that cannot be repaired.
   5. Disaster Recovery
      1. Mission Essential Functions
      2. Identification of Critical Systems
      3. Disaster Recovery Planning
         1. Disaster Recovery Plans (DRPs):
            1. A plan that details the policies and procedures concerning the recovery and/or continuation of an organization's technology infrastructure.
         2. Business Impact Analysis:
            1. The examination of critical versus noncritical functions; part of a business continuity plan (BCP).
         3. Recovery Time Objective (RTO):
            1. In business impact analysis, the acceptable amount of time to restore a function.
         4. Recovery Point Objective (RPO):
            1. In business impact analysis, the acceptable latency of data.