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Can replication replace backup?

Well, since you ask...

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Claus Egge

Storage Analyst

The debate about Replication versus Backup suggests significant waste in storage. But the purpose behind copying data back and forth is not trivial and multiple copies are rarely pointless. Duplication can conversely be inefficient and overkill.

Backup can be used both for day-to-day recovery of files and for disaster recovery of entire systems.

Total copies of systems for backup and disaster recovery (BC/DR) purposes are intended for re-establishing entire systems as quickly as possible. High calibre BC/DR relies on synchronous or asynchronous replication between disk arrays. The term "replication" here refers to a continuous trickle of updates from source to target. Less ambitious designs may use tape or disk for point-in-time backup, but again the BC/DR backup should be used only for this purpose when a serious incident has happened.

With regard to day-to-day backup the ability to recover subsets and earlier versions of files is intended to be invoked for restoration at will or through automation. These backups are typically performed per application type, but should be kept separate from BC/DR. The backup applications can be highly sophisticated and employ advanced snapshot techniques or CDP (Continuous Data Protection) for instance. The capacity and performance can further be optimised through de-duplication.

Many IT sites still rely on magnetic tape, a key reason being that it enables off-site BC/DR especially for small and medium businesses. But even in a multi-site set-up customers are still comfortable with tape serving as portable and mechanically simple storage containers. Also, certain types of data and certain industries are governed by regulation dictating retention periods, which favour tape. Yet, there is no technical reason for not eliminating tape entirely.

Strictly speaking, a backup can be described as an amount of data or a point in time and whether it is created by backup software or some form of snapshot process is irrelevant. Replication can be described as the mechanism by which a remote backup target gets updated. On that basis replication can not replace backup as it is an essential complement to backup in creating a disaster recovery system.

Claus Egge is a storage analyst whose IT career started in IT Operations in his native Denmark where he managed storage environments. In 1991 Claus moved to the UK, becoming a storage analyst at Market Research company IDC, eventually managing the entire European storage market research practice. He became an independent analyst in 2010.

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