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CDP: Blurring the Line Between High Availability and Backup


Josef Pfeiffer

For as long as people have been protecting data there have been a myriad of products to help. High availability and backup are two general categories of products that can assist but they offer very different benefits.  On one end of the spectrum, high availability includes technologies like clustering, replication and shared file systems and they really allow for near zero recovery time when a problem occurs.  If a clustered server fails, then it automatically fails over to another server and helps to ensure the application stays up and running.  What high availability lacks is the ability to roll back to older points in time.  For this reason, high availability is almost always complemented with backup products that make additional copies of the data at specific moments in time. Together they help create recovery point objectives and recovery time objectives that can be tailored to the importance of the data.

Recently however, continuous data protection (CDP) has started to blur the lines between these two separate product categories. CDP is often correctly viewed as a different way to protect data.  It tracks all changes to a disk continuously block-by-block, as opposed to scheduled points in time. CDP’s key differentiator is how it changes recovery.  Backup products always store data in a different location, whether on tape or disk (deduplicated), it has to go through some process to get copied back to its original location.  You simply can’t run your server or application off of that backup storage.  

CDP changes this however by virtualizing the backup storage and presenting read/write volumes that can be used.  The mere fact that you no longer have to copy data back to another location means that your recovery time is dramatically reduced to near zero. Sound familiar?  Yep, just like high availability.  Can’t find replacement storage in production when a problem occurs?  No problem, just run the application off a CDP server until a more permanent recovery option is available and you can fail the data back once things are fixed.  The benefit is near zero downtime. If the corruption is copied to CDP, you can simply rewind to a previous moment in time and present a virtualized disk volume of how that original volume looked at any point in time.

While there usually is a trade off between recovery points and recovery time, CDP gets pretty close to reaching near zero on both.  While not every application needs high availability or CDP, it is becoming an easy option to add to your existing data protection environment.

  • Joe_Kelly

    Nice Post Josef. Is Symantec's offering appliance based or purely host based? Does the splitting occur @ the host or within your SAN Fabric? If host based, what performance penalty is imposed? Just trying to determine the differences between EMC's RecoverPoint and what Symantec push's. Thanks for your time.

  • Joe_Kelly

    Nice Post Josef. Is Symantec's offering appliance based or purely host based? Does the splitting occur @ the host or within your SAN Fabric? If host based, what performance penalty is imposed? Just trying to determine the differences between EMC's RecoverPoint and what Symantec push's. Thanks for your time.

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