MTPD, just to remind you, stands for Maximum Tolerable Period of Disruption. It’s a metric that gets less publicity than RTO (recovery time objective) and RPO (recovery time objective) and there is a reason, if not an excuse, for that. Definitions for MTPD usually sound simple: for example, “The maximum time an activity or resource can be unavailable before irreparable harm is caused to the organization.” The more complicated part is in the measurement of MTPD. Gauging irreversible damage in terms of job security of employees, legal liabilities, reputation and/or shareholder value is as much an art as a science. Furthermore, that simple definition may also be hiding more than meets the eye.
The overall concept of MTPD (or MTPoD, if you prefer) is a good one. You need to know MTPD for different key organisational activities, so that you can concentrate on priority items (lowest MTPD, for instance) and select solutions that fix things before the MTPD expires, not after. Business impact analysis (BIA) is typically the way to determine MTPD. Business objectives and risk analysis should also be prime factors in determining RTO and RPO. However, rightly or wrongly, figures for these two metrics are often influenced by existing technology and resources, which set limits on what can be accomplished, making them easier to calculate.
What MTPD does not describe is the amount of damage that may be done before it becomes irreversible. Think about the following different situations. In the first, a legal requirement for periodic reporting for example, damage can be considerable if MTPD is exceeded, but almost zero if a solution is implemented before MTPD expires. In the second, a production problem slows output to a crawl. Customers will only wait so long before moving to one of your competitors, and some may move before MTPD expires. While you might be able to win them back in the future, you lose revenue and goodwill, at least in the short term. In summary, MTPD sounds simple, but deserves some thought and scrutiny if you want to get it right.