An important part of planning for disaster recovery is setting objectives for recovering. Your objectives will have a major impact on the cost and effort of the recovery, as well as help you choose among recovery alternatives.
The Recovery Time Objective (RTO) specifies how soon you will be up and running after a disaster. More technically, it is the time your organization will need to recover. Organizations may have multiple RTOs depending on the data involved. For example one RTO may specify how long before the major functions of the enterprise are back on line while a second, longer, RTO will determine how long until everything is fully recovered.
The Recovery Point Objective (RPO) determines how old the recovered data will be. This can be anywhere from a few seconds in the case of a sophisticated (and expensive) remote mirroring system to several hours, or even days, for less critical data. Like the RTO, the RPO is often assigned by functions, with critical functions -- such as transaction processing -- having short RPOs and less immediate functions recovering to a point further back in time.
The Network Recovery Objective (NRO) is, effectively, how long before you appear recovered to your customers. More technically, it is the time needed to recover or fail over network operations. NRO includes such jobs as establishing alternate communications links, reconfiguring Internet servers, setting alternate TCP/IP addresses and everything else to make the recovery transparent to customers, remote users and others.
IBM gives definitions of useful disaster recovery concepts at: http://publib-b.boulder.ibm.com/Redbooks.nsf/RedbookAbstracts/tips0047.html?Open.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.