This article describes the methods that can be used in Microsoft Windows to reclaim dead space.
In Windows dead space is left behind when you delete a file or shrink a SQL database for example.
How to find dead space for Windows Server 2012/2012 R2
Compare Windows file system usage to LUN usage in array.
Windows Server 2012/2012 R2 is capable of identifying the provisioning type and the UNMAP and TRIM capability of a disk. Space reclamation can be triggered by file deletion, a file system level trim, or a storage optimization operation.
You can check if your disks are identified as thin or not from “Defragment and Optimize Drives” tool. If your thinly provisioned disk does not identify as thin disk in Windows check with your array vendor. Array firmware update might be needed to enable support.
You can read more about Windows Server 2012 unmap from here.
More information about Windows Server 2012/2012 R2 Defrag can be found here.
Windows Server 2003/2008/2008 R2
Older Windows versions does not include automatic UNMAP support. Third party tools can be used to reclaim space.
EMC StorReclaim is a command line utility to UNMAP allocated but unused space from storage array. It can be used in physical servers and virtual servers for LUNs which are presented directly from storage array. To get a the tool contact your EMC representative.
Supported operating systems:
Windows Server 2003 x86/x64
Windows Server 2008 x86/x64
Windows Server 2008 R2
Windows Server 2008 R2 with SP1