Q. How can I check how much space I will save if I use data deduplication in Windows Server 2012 and above?
A. Microsoft provide a tool, DDPEval.exe, which when used will provide a break down of the savings that will be had if data deduplication is used. The tool can be used against a file share, a driver or a specific folder. Below is an example execution and pay attention to the Optimized files size and space savings details:
PS D:\> ddpeval . Data Deduplication Savings Evaluation Tool Copyright (c) 2013 Microsoft Corporation. All Rights Reserved. Evaluated folder: . Evaluated folder size: 78.30 GB Files in evaluated folder: 13 Processed files: 8 Processed files size: 78.30 GB Optimized files size: 13.45 GB Space savings: 38.41 GB Space savings percent: 74 Optimized files size (no compression): 26.83 GB Space savings (no compression): 25.03 GB Space savings percent (no compression): 48 Files excluded by policy: 5 Small files (<32KB): 5 Files excluded by error: 4 Sharing violation: 4
More information on the tool can be found at https://technet.microsoft.com/en-us/library/hh831700.aspx. This is very useful to estimate the benefit deduplication would bring to a volume.