When is backup not enough? I saw an interesting blog on this from ZDNet on a case where backup was not enough. There are plenty of case, such as when the data itself is just not correct? What about when part of your data is loaded incorrectly, or even comes from a suspect source?

Imagine if a salesman or group of salesmen were upset with the company and spent two weeks entering fake orders, along with real ones, into your database under different accounts. A backup doesn't necessarily help you here in restoring your database to a good, usable state.

One of the dangers of backups, or an HA technology like mirroring that moves changes to a remote location in near real time, is that changes to data are moved immediately. Corruption, incorrectly entered data, there are other potential changes to the database that can't easily be recovered from a backup. Or that you don't want to use a backup to recover from.

This is a place where it becomes important that you can easily segregate out changes to your data and perhaps undo them. A way of recovering your system to a good state without a full database restore. Log reading tools can help here, as can good meta data on ETL type operations. Even a well designed audit system could potentially allow you to recover to a good known state.

Ultimately it will depend on the knowledge of your business people to determine what data should be in your system. They might need to check with customers to verify orders, or conduct an inventory to determine what values should have been written on that corrupted page. In most cases, this will involve manual work, and unhappy database users.

People depend on your database, and it's important you do you best to secure data, cleanse it, try to protect it from corruption, and more. But we also need to recognize that just doing backups might not be enough, and your definition of "disaster" might want to include something besides a server crash.

Steve Jones

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