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Backup in a snap: A guide to snapshot technologies

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The downside to incremental snapshots is that they're dependent on the underlying baseline technology used in the first snapshot (copy-on-write, redirect-on-write, clone/split-mirror or copy-on-write with background copy). If cloned, the first snapshot will take a while; if COW, there will be a performance penalty on writes to the original data, etc.

Continuous data protection (CDP)

CDP was developed to provide zero data loss recovery point objectives (RPOs) and instantaneous recovery time objectives (RTOs). It's similar to synchronous data mirroring except that it eliminates the rolling disaster (a problem in the primary data is automatically a problem with the mirrored data long before human intervention can stop it) and protects against human errors, malware, accidental deletions and data corruption.

Continuous data protection is like incremental snapshots on steroids. It captures and copies any changes to the original data whenever they occur and time stamps them. It essentially creates an incremental snapshot for every moment in time, providing very fine-grain recoveries. Some CDP implementations are both time and event based (such as an application upgrade). A good way to think of CDP is as a journal of complete storage snapshots.

CDP is an excellent form of data protection for email, databases and applications that are based on databases. The ability to roll back to any point-in-time makes recoveries simple and fast. FalconStor's

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IPStor is an example of a storage system and/or virtualization appliance that provides CDP.

With more and more data to protect and often less time to do it, snapshots will play a bigger role in data protection and daily storage operations. Although the differences among snapshot technologies may seem subtle, how they operate in your environment could have a significant effect on the level of protection provided and how quickly recoveries can occur.

BIO: Marc Staimer is president of Dragon Slayer Consulting.

This was first published in October 2009

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