The ConfigMgr team recently published a blog post on the supported use of Data DeDuplication with ConfigMgr 2012 R2. Here is a Geek's summary of the 1500 word blog post:
1. Data DeDuplication is awesome!
2. ConfigMgr 2012 R2 supports Data DeDuplication on the following ConfigMgr folders only:
- Content Library (SCCMContentLib)
- SMSPKGx$
Note #1: This means you cannot have your source locations in a Data Deduplication scenario, only the above folders.
Note #2: Since Data DeDuplication is enabled on a per volume basis, you need to exclude any other ConfigMgr folders you may have on that volume.

Excluding ConfigMgr folders other than the supported E:\SCCMContentLib and E:\SMSPKGE$. Please note I also excluded the sccm_sources folder which is my source location.
PowerShell is King
Fellow deployment geek, David O'Brien, has written has nice post on configuring DeDup for ConfigMgr using PowerShell: https://david-obrien.net/2014/02/enable-deduplication-powershell-configmgr-exclusions/
/ Johan