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A Data De-Duplication Survival Guide: Part 1: Page 6 of 7

Another challenge that single instance storage doesn't address is that there are often multiple backup sources for similar data sets. For example, the backup administrator may back up Exchange with the backup software’s Exchange module; the Exchange administrator may also back up the Exchange stores with a separate utility. No data reduction happens here, since the backup software never sees the backups created by the standalone utility.

In both cases (apps with frequent small changes and multiple backup sources), a data de-duplication system operating at a block level would identify the redundant blocks and reduce the storage impact even though the backup source (backup application or Exchange utility) is different.

Software suppliers that use this single instancing technique will claim that this storage method is better suited for recovery, implying that there are some restore performance issues with de-duplication systems. While there may have been some recovery performance issues with data de-duplication systems from some suppliers, when the system is designed with the correct architecture there should be no measurable impact on performance as a result of the data de-duplication process.

In a real world data center, there are simply too many other bottlenecks between backed-up data and the source server for recovery from a general purpose data de-duplication system to be the problem. If the recovery performance requirement exceeds the ability to recover from disk, then other high-availability solutions, like clustering or active targets, should be considered. (An active target is a backup target application that can be browsed and read like a normal file system.)

Finally, the method of using single instancing assumes the use of a single software application for all backups, archives, and other data management functions and across all data types. This is not practical. While many backup software suppliers do offer some sort of additional components beyond just backup, there are varying degrees of functionality with these additional modules, and most customers in reality are going to have separate solutions for backup and archive, as well as applications for particular platforms (such as VMware). There will also be a limit to how much development a software manufacturer will invest in a module for a unique database or operating system.