SQLServerCentral Editorial

Flexibility in DR

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Disaster recovery is a topic that many people who work with databases find important. DBAs work to ensure their systems are highly available while practicing the skills needed to recover them in the event of a disaster. While we often practice the failure of a complete server or database, we sometimes forget there can be other issues for which we need to plan.

I ran across a story about a data center outage in London, which was similar to an incident I experienced. In this case, a piece of power equipment failed and systems lost network access. While many of us aren't responsible for the network, we certainly would still receive complaints if the database wasn't available.

In my situation, I was in a data center watching some workman service UPS systems. At the time I was a manager of database systems and thought they had things under control. I left the data center and went downstairs, only to audibly notice when the power dropped that all servers seemed to stop running. Similar to the London outage, a switch that was supposed to change power from one set of UPSes to the other failed. Our entire global infrastructure for 10,000+ people and who knows how many customers went down. This was in the pre-cloud era where we acted as our own cloud. And not very well.

There are systems outside of our databases that we depend on. We might not be responsible for them, but we ought to ensure they are a part of our disaster recovery plans and account for various things going wrong. At the very least, we ought to question whether power, network, storage, and more are adequately prepared for major issues.

We also need to think about minor issues. Atlassian had a major outage, at least for some customers, and they realized that they hadn't planned to recover parts of their databases. A similar issue might occur for any of us, where we might have to restore parts of a database, whether that's a table, partition, or a series of rows. Corruption or human error might result in a set of data that's unreadable or even gone. I know I've accidentally caused data issues, and I'm careful. I learned to recover from my own mistakes and anticipate those of others. I practice not only full restores but how to copy over part of table from another location.

A disaster is a major problem, but it might only affect a minor part of our systems. We need to ensure we are ready for any size or scale of problem and be ready to adapt our thinking and process to meet the disaster with the appropriate actions.

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