What is RPO, RTO, WRT, MTD?

As this was the toughest topic for me to explain that What is RPO, RTO, WRT, MTD?  so today i will explain this topic in the same way in which my colleague explained me and i was able to understand too.
RPO = Recovery Point Objective
RTO = Recovery Time Objective
WRT = Work Recovery Time
MTD = Maximum Tolerable Downtime

Stage 1 : Business as Usual
At this stage all systems are running production and working correctly.

Stage 2: Disaster Occurs
On a given point in time, disaster occurs and systems needs to be recovered. At this point theRecovery Point Objective (RPO) determines the maximum acceptable amount of data loss measured in time. For example, the maximum tolerable data loss is 15 minutes.

Stage 3: Recovery 
At this stage the system are recovered and back online but not ready for production yet. The Recovery Time Objective (RTO) determines the maximum tolerable amount of time needed to bring all critical systems back online. This covers, for example, restore data from back-up or fix of a failure. In most cases this part is carried out by system administrator, network administrator, storage administrator etc.

Stage 4: Resume Protection
At this stage all systems are recovered, integrity of the system or data is verified and all critical systems can resume normal operations. The Work Recovery Time (WRT) determines the maximum tolerable amount of time that is needed to verify the system and/or data integrity. This could be, for example, checking the databases and logs, making sure the applications or services are running and are available. In most cases those tasks are performed by application administrator, database administrator etc. When all systems affected by the disaster are verified and/or recovered, the environment is ready to resume the production again.

The sum of RTO and WRT is defined as the Maximum Tolerable Downtime (MTD) which defines the total amount of time that a business process can be disrupted without causing any unacceptable consequences. This value should be defined by the business management team or someone like CTO, CIO or IT manager.

This is of course a simple example of a Business Continuity/Disaster Recovery plan and should be included in your Business Impact Analysis (BIA).

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