As companies depend more and more on computer applications for day-to-day business operations, the cost of downtime has increased. Many small and medium businesses are under pressure to provide continuous operations of business applications and databases on a small budget, because of these increasing costs of downtime.
High availability goes beyond simple data replication to a remote system and provides real rollovers to hot spare servers from production machines.
A complete high availability / disaster recovery solution should include recovery scenarios that protect against not only site failure in the case of a disaster, but also protect from rolling disasters.
DR is related to, but not the same thing as, high availability. High availability focuses on maintaining constant access to applications via techniques such as database mirroring and server clustering. DR focuses on the recovery of such access after a disaster or other significant disruption. Thus, to maintain high availability, IT decision makers should ensure that DR receives the same focused attention that considerations related to high availability and other business-critical requirements receive.
Recovery can be expressed as a recovery time objective (RTO) or a recovery point objective (RPO). An RTO is the desired period after which functionality returns to normal following a disruption. An RPO is the desired point to which data can be restored after a disruption. IT and business decision makers should collaborate closely to arrive at the optimum balance among business goals, desired RTOs and RPOs, and DR costs.