Reclaiming Storage on a Windows VM with a VirtIO SCSI Disk

This page explains how to reclaim unused storage space from a Windows VM that uses a VirtIO SCSI disk.

Overview

A Windows virtual machine using a VirtIO SCSI disk may not return unused storage space to the cluster running SC//HyperCore™ HyperVisor after data is deleted within the guest operating system. This happens when TRIM is disabled or a retrim hasn’t run. This page shows how to check TRIM support, enable it if needed, and run a manual retrim to reclaim the space.

Requirements

• SC//HyperCore 9.6 or later
• Virtual disk configured as VirtIO SCSI
• VirtIO drivers installed in the guest OS
• Administrative access to the Windows VM

Procedure

1. Verify TRIM Support

Open an elevated Command Prompt and run:

fsutil behavior query DisableDeleteNotify

Expected result:

DisableDeleteNotify = 0

Meaning:

2. Enable TRIM (If Necessary)

If the previous command returns DisableDeleteNotify = 1, run this command to enable TRIM:

fsutil behavior set DisableDeleteNotify 0

3. Consolidate Free Space

Before you run the reclaim, consolidate fragmented free space.

Run:

defrag C: /U /V

This gets the filesystem ready to reclaim as much storage as it can.

4. Issue the Reclaim (TRIM) Operation

After defragmentation finishes, run:

defrag C: /L

This sends a retrim command to the storage device, so it can release unused blocks back to the SC//HyperCore cluster.

Alternative Method (PowerShell)

You can also run the retrim from PowerShell:

Optimize-Volume -DriveLetter C -ReTrim -Verbose

This runs the same TRIM operation as defrag C: /L.

Notes

• For best results, run the defrag and retrim operations one after the other.
• Storage reclamation does not reduce the virtual disk size. It releases unused blocks back to the cluster’s storage pool instead.
• Windows may issue TRIM operations on its own during scheduled storage optimization tasks. But a manual retrim can help after you delete a lot of data.