Recovery Time Objective (RTO)
The recovery time objective (RTO) is the maximum tolerable length of time that a computer, system, network, or application can be down after a failure or disaster occurs. The RTO is a function of the extent to which the interruption disrupts normal operations and the amount of revenue lost per unit time as a result of the disaster. These factors in turn depend on the affected equipment and application(s). The RTO is measured in seconds, minutes, hours, or days.
Numerous studies have been conducted in an attempt to determine the cost of downtime for various applications in enterprise operations. These studies indicate that the cost depends on long-term and intangible effects as well as on immediate, short-term, or tangible factors. Once the RTO for an application has been defined, administrators can decide which disaster recovery technologies are best suited to the situation. For example, if the RTO for a given application is one hour, redundant data backup on external hard drives may be the best solution. If the RTO is five days, then tape, recordable compact disk ( CD-R ), or offsite storage on a remote Web server may be more practical.
Recovery Point Objective (RPO)
The recovery point objective (RPO) is the age of files that must be recovered from backup storage for normal operations to resume if a computer, system, or network goes down as a result of a hardware, program, or communications failure. The RPO is expressed backward in time (that is, into the past) from the instant at which the failure occurs, and can be specified in seconds, minutes, hours, or days.
Once the RPO for a given computer, system, or network has been defined, it determines the minimum frequency with which backup s must be made. This, along with the recovery time objective ( RTO ), helps administrators choose optimal disaster recovery technologies and procedures. For example, if the RPO is one hour, backups must be made at least once per hour. In this case, external, redundant hard drives may prove to be the best disaster recovery solution. If the RPO is five days (120 hours), then backups must be made at intervals of 120 hours or less. In that situation, tape or recordable compact disk ( CD-R ) may be adequate.