Posts Tagged ‘VNX Deduplication’

VNXe Deduplication and Compression

August 22, 2011

I had to do some digging recently to get some technical details on the deduplication technology imbedded in the EMC VNXe arrays so I thought I’d share it.

Summary

The file-level dedup on the new VNX arrays is only for Shared Folders and NFS datastores.  This deduplication is policy driven and utilizes both file deduplication (single instancing) and compression.  The compression of files has NO impact on data sharing.  The deduplication acts on whole files and does not look at the metadata.  In addition, shared folders and NFS datastores can have different dedup settings and the dedup will work in conjunction with replication, snapshots and file level retention.

Policy Engine

The policy engine which controls deduplication runs automatically and is governed by high and low CPU watermarks for the Datamovers.  When the CPU is below 40% the policy engine runs at full speed.  When CPU utilization is between the low and high watermarks (40 – 75%) the policy engine is throttled.  CPU utilization above 75% will cause the policy engine to go into a paused state until the utilization drops.

There are 2 main settings that can be configured in the policy engine, the File Extension Exclude list and the Path Exclude list.  Here you can set certain file types or data paths to be excluded from deduplication. 

Additional Thresholds

The threshold for deduplication on files is 30 Days.  Files that have been read or modified in the last 30 days are exluded from the deduplication process.  There is also a file size threshold to be aware of.  Files greater than 8TB and smaller than 24KB are excluded from the deduplication process also.

So, while you certainly won’t see deduplication ratios like you would on DataDomain or Avamar appliances the VNX deduplication can prove to be very useful and save you precious production storage space.  Best of all, VNX deduplication is easy to turn on and manage through the Unisphere GUI. 

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