Disaster Recovery (DR) is the act of restoring infrastructure and services after a disaster that stops either a single server, or even a complete data centre. Many techniques can be employed to mitigate the effects of any level of disaster. From having local hot standby servers to take over if a failure occurs, through to mirroring a complete data centre infrastructure to another geographic location, to have it available should a primary data centre be taken offline. The requirements for DR are very unique to each organisation. Some services will be essential to allow the organisation to function, and must be made available immediately. Other services will be less mission critical and can be brought back online in a controlled manner at a later time.