Disaster recovery involves the anticipation of major business outage, and the contingency planning to avoid business loss in revenue, customers or sales.
All of the technology components that make up your enterprise applications should be carefully considered against loss. What happens if this database server disappears? Do we have all the data backed up somewhere? Have we tested that backup to restore it? How long does it take to restore? Can we reconnect the application to said database? What if the network goes down? How about if the whole datacenter goes out?
Planning for disaster recovery is important whether you’re hosted in-house or with a hosting provider. Consider Amazon’s EC2 outage in April. Various availability zones went out. Were affected customers to have their database backed up properly – with offsite & tested copies, and further if they had other components such as webserver document roots, software configurations, etc they would be able to rebuild their entire infrastructure in an alternate availability zone or region. Remember it was only a small component of Amazon Web Services which was out.