Why RPO Doesn’t Matter
January 11th, 2012 | 
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Transaction Volume is Rarely Even
When I ask the question, “What’s your RPO?” I typically get an answer like “We’ve got an RPO of 5 minutes.” If I ask “How much data are you willing to lose?” I’ll hear a similar answer. But if I ask someone, “How much data is in your storage system?” they don’t answer me in minutes.
The data created by the mission-critical applications that support businesses don’t get updated in an even, regulated way. The update rates are almost always highly variable, full of transaction peaks and valleys. The peaks can happen during predictable times, like a holiday shopping season, and during unexpected times, like when there is panic buying before a hurricane.
That’s the not-so-funny disconnect between data and disaster recovery. We don’t measure data in minutes. We measure it in GBs. Wouldn’t it be better to set our snapshots and our recovery points based upon how much data has changed, instead of how much time has passed?
I have to credit our CTO, Dr. Alex Winokur, for helping me think this through. But, I’ve decided that, unless your RPO is zero, RPO doesn’t matter. Instead, we need to make sure we’ve protected the data to the very last byte.
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When a system is down, does a disgruntled customer ever ask, “how much data are you recovering in order to serve me?” It’s a totally irrelevant factor. The recovery time is a business parameter, an output from consideration of customer requirements, for which data size is not an input. Asking the data size gives the company an excuse to worsen their recovery performance, rather than re-thinking the problem to meet real business objectives.
David,
Thanks for the comment. I agree, no customer would ever ask, “How much data are you recovering in order to serve me?” Suppose, though, that you are able to meet a demanding, very short RTO window, successfully recovering an application that enables you to process new transactions, but, as with most organizations, your data replication and data protection process guarantees that you will lose some recent customer data, data that answers questions like:
“Where’s did you ship my luggage?”
“When will my package arrive?”
“What was on that MRI?”
“What was the dosage for my medication?”
“Did you confirm my reservation?”
“Did you receive my order?”
“Do I have a seat on the next train?”
Then your customer will care very much about the fact that you lost THEIR data, and you will care about how many customers were affected. We recently showed one airport that the loss of a few hundred megabytes of data generated in a few minutes would impact thousands of passengers.