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Disk space recovery with Hyper-V
40 Dell EMC SC Series: Microsoft Hyper-V Best Practices | CML1009
5 Disk space recovery with Hyper-V
In Microsoft Windows, deleting a file just removes the file pointer, not the actual data itself. The operating
system will report this deleted space as free to be overwritten by new data. However, there are situations
where the SC Series will not return the deleted space to the SC Series array page pool to be used elsewhere.
This can result in inefficient use of the SAN storage capacity.
There are two ways to automatically recover deleted space on the array:
• Native Trim/Unmap support
• Install the SC Series server agent on the host server (works in concert with the daily Data
Progression cycle to recover space)
For more information on Trim/Unmap and the SC Series server agent, see the Dell EMC SC Series and
Microsoft Windows Server best practices guide.
5.1 SC Series support for Trim/Unmap with Hyper-V
Hyper-V environments also support TRIM/Unmap natively given the following conditions:
• The Windows Server OS (for hosts or clustered nodes) must be version 2012 or newer.
• Physical volumes (including boot-from-SAN disks, cluster shared volumes, direct-attached and pass-
through disks) must be basic disks formatted as NTFS volumes. TRIM/Unmap is not supported with
other formats such as ReFS.
• SC Series SCOS must be version 6.3.1 or higher.
• Virtual hard disks support TRIM/Unmap given the following conditions:
- The cluster shared volume (or other data volume) that hosts the virtual hard disk is a basic disk
formatted as an NTFS volume.
- The guest VM OS is Windows Server 2012 or newer.
- The guest VM is a generation 2 VM.
- The guest VM OS formats the virtual hard disk (fixed or dynamic) as a basic disk NTFS volume.
Note: The Dell Storage Manager (DSM) server agent can be installed on a Windows Server 2012 or newer
host, but the disk space recovery feature is disabled by default as native support for Trim/Unmap is assumed.
5.2 Space recovery with 2008 R2 Hyper-V
The DSM server agent can be installed on Windows Server 2008 physical hosts or guest VMs. It enables disk
space recovery if the following conditions are met:
• Recovery is possible from physical volumes (including boot-from-SAN disks, and direct-attached and
pass-through disks).
• Disks must be basic disks formatted as NTFS volumes. Other formats such as ReFS are supported
with SC Series but not for disk space recovery.
Disk space recovery will not work on the following types of drives/volumes with Windows Server 2008 R2
Hyper-V:
• Virtual hard disks (dynamic or fixed). If free space recovery is highly desirable for a guest VM
scenario, then present storage as a basic disk formatted as NTFS to guest VMs as pass-through or
direct-attached disks.