Disaster Recovery can be described as a tool, or safeguard, that ensures that the continuity of operations is maintained regardless of possible scheduled or unscheduled outages.
A scheduled outage can be anything that requires a planned data-center outage for an upgrade, a planned take down of a web front-end or an entire SharePoint farm.
An unscheduled outage includes any kind of fail-over scenario in which administration is not given the option to prepare or manually stop replication this includes power outages, network issues, and natural disasters.
In the event of either a planned and unplanned outage, a Disaster Recovery environment is key to have in place, as it ensures that COOP is maintained.
NOTE: our recommendation is to set up a Disaster Recovery environment using one-way replication. A DR environment is strictly for the purpose of backing up and recovering all content in the event of a planned or unplanned outage.
Replication is initially set up using a one-way connection that replicates all content regularly from your main server to your DR environment. In the event of a planned or unplanned outage on this main server, pause the one-way connection from your main server to the DR server, and direct all of your users to your DR environment. Here end-users can continue to use SharePoint as per usual, where all changes will be replicated and placed in a queue. Once your main server is back up and running, set up a connection from your DR to your main server and then pushing the event queue with all changes back over.