Disaster

b.- What constitute a disaster? Or how can You define a disaster in such a way, that both customer and possible vendor know when to activate the DR plan. 

Answer:

A disaster is basically a situation when the activities are disrupted more then their RTO. You can read more about this here “Activation procedures for business continuity plan” : https://advisera.com/27001academy/blog/2011/09/26/activation-procedures-for-business-continuity-plan/. Keep in mind that “Disaster recovery” and “Business continuity” are not the same (basically the first is a part of the second). To know more about this, please read this article “Disaster recovery vs Business continuity” : https://advisera.com/27001academy/blog/2010/11/04/disaster-recovery-vs-business-continuity/

The RTO is the Recovery Time Objective, this means: defined time in your business which a business process must be restored after a disaster. If you need more information about this , please read: “How to implement business impact analysis (BIA) according to ISO 22301” : https://advisera.com/27001academy/knowledgebase/how-to-implement-business-impact-analysis-bia-according-to-iso-22301/

Now, do you need to write a Business Continuity Plan? Please read this article “How to write business continuity plan” : https://advisera.com/27001academy/blog/2010/04/08/how-to-write-business-continuity-plans/

Also can be interesting for you read this article “Disaster recovery site – What is the ideal distance from primary site?” : https://advisera.com/27001academy/knowledgebase/disaster-recovery-site-what-is-the-ideal-distance-from-primary-site/