Introduced in Windows Server 2008 and enhanced in Windows Server 2012 and 2012 R2, the Disk Deduplication tool is an exemplarity tool used by IT professionals to save storage space amidst the infrastructure they manage. The storage space saved is reclaimed from duplicate files being removed utilizing said tool.  Enabling data deduplication is an easy process and has been detailed here on CANITPRO.NET in a blog post written by Pierre Roman entitled:
Step-by-Step: Enabling Data Deduplication on Windows Server 2012 Volumes

During our recent CANITPRO Camp offering entitled "Managing your Datacenter with Windows Server 2012 R2 & System Center 2012 R2" a tale is told about an eager IT administrator who was excited to learn about the data deduplication tool and the possibilities it could create.  Said IT administrator was so excited that upon return they created a new Windows Server 2012 R2 evaluation image, joined it to the live domain and ran the disk deduplication tool.  What they immediately discovered was at 80% retrieval of disk space previously occupied by duplicate files. However what they also discovered was the running said task at a large financial organization without having the new server or tool submitted for approval was not a wise idea.  It is always advised to test in lab and submitting results for approval before auctioning on live data.  However, there is a way to test what deduplication efforts could possibly result in without affecting live data with the use of the Deduplication Evaluation Tool.  Further more this tool can be run on Windows Server 2008 and higher as well as Windows 7 and higher to test and report on duplicate data

Note: The Deduplication Evaluation Tool cannot be utilized on system and/or boot volumes or a volume that already has data deduplication enabled

The Deduplication Evaluation Tool is enabled via a file located in the windows\system32 directory called ddpeval.exe on Windows Server 2012 machines with disk deduplication enabled.  An IT administrator would have to run the following command to invoke the tool against a volume inside of the command prompt as Administrator:
ddpeval.exe D:
While in this example the "D" drive is used, an IT administrator could point the command to any non system and/or boot volume, folder or even against a directory on a remote server. More options surrounding the Deduplication Evaluation Tool can be listed by typing the following command:
Ddpeval.exe /?
Disk deduplication can be a great enabler for any organization to retrieve space within their organization's storage infrastructure. The Deduplication Evaluation Tool allows IT administrators to better report on what results would be should the tool be enabled on live data.  Be sure to also checkout Microsoft Virtual Academy has it offers a Managing Data Deduplication lesson to further prepare IT professionals to properly harness the tool.