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Can replication replace backup?

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You the Expert We are asking Reg reader experts - and a chief technology officer - to have a look at interesting issues in storage. The first topic is:

Can replication replace backup?

Backup started as saving a copy of data to tape. For many users it now means saving a copy to disk, either as a straight file backup or as a virtual tape backup. In both instances data is being moved from one disk to another. That’s what replication does too, but without the complexities of backup software and restoration using backup software.

Does this mean you can dump your backup software and rely completely on the much simpler replication idea?

We asked four storage experts what they think about this - and you can read their musings below. But we are very interested in your thoughts too. We are keen to expand our line-up of Reg experts. Show us what you are made of!

Chris Evans

Chris Evans

Independent storage consultant

Initially, the obvious answer to this question is no; replication can’t replace backup; that’s not what the technology was designed for. Replication was developed to migrate data between storage arrays in the event of a physical failure in a storage device or with the site in which the storage device is located. The process of replication creates an exact replica of data at the source location. This is achieved either synchronously or asynchronously; effectively as soon as a change is made on the primary array is it permanently made on the secondary.

Traditional replication goes against the premise for which backups are taken - to recover to a point in time at which data was lost or corrupted. The second point (corruption) is probably the most important reason why traditional replication can’t replace backup - corrupted data would be replicated to the remote site before there had been any chance to identify it or to stop the replication that had occurred.

However, of course, replication is no longer simply transmission of changed blocks of data from storage device to another. Continuous Data Protection (CDP) logs changes in primary data and stores those changes for a finite period of time, enabling recovery to be made at a secondary site to any time in the past - assuming enough data has been retained. This is fundamentally different from traditional replication where the changes are usually simply overwritten immediately.

In summary, traditional replication will not replace backup - however, CDP-style replication may just have a chance.

Chris M Evans is a founding director of Langton Blue Ltd.. He has over 22 years' experience in IT, mostly as an independent consultant to large organisations. Chris' blogged musings on storage and virtualisation can be found at www.thestoragearchitect.com.

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