Tip of the Day: Dedup'ing VHDx files


Today’s Tip…

In Windows Server 2012, dedup was more focused on consolidation for files at rest and that have gone unchanged for x days, where x=5 by default.  Windows Server 2012 R2 provides deduplication that consolidates files which are more in use, possibly with outstanding open handles.  Dedup does this by skipping hot ranges of a file during the optimization job.  Hot ranges are defined as a range of a file that has been modified with using the threshold time period.  Deduplication determines file heat by consuming the USN journal.  A hot range bitmap is created based on the consumed USN journal records.

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NOTE:  Since the USN journal is disabled by default, it will now be enabled when the Deduplication role is enabled for that volume.

The access pattern of a typical VHD/VHDx file is such that a large portion is not changing, at least not frequently, and we classify this region as being cold in the context of this feature.  A relatively small portion of the file is under constant flux due to the fact that it contains the VHD metadata, or the data corresponds to the workload that the VHD/VHDx file is being used for - being classified as hot.


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