ReFS volume space reclamation

Adin Mohhamed 20 Reputation points
2026-09-04T07:48:48.7233333+00:00

Dear Microsoft Support Team,

I hope you are doing well.

We are encountering an issue with space reclamation on an ReFS volume hosted on a SAN array. After deleting several terabytes of data, the unallocated space is not being returned to the SAN storage pool.

We would like to know how to manually trigger TRIM/UNMAP operations using the Optimize-Volume -ReTrim command to reclaim unused space.

Environment Details:

File System: ReFS

Storage Type: SAN Array

Data Deleted: Multiple terabytes

Issue: Unallocated space not released back to SAN

Could you please advise on the correct procedure or parameters required to force TRIM/UNMAP requests manually ? Additionally, please confirm if any prerequisites or storage vendor configurations are needed for successful space reclamation.

Windows for business | Windows 365 Business
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  1. VPHAN 42,425 Reputation points Independent Advisor
    2026-09-04T08:25:00.6966667+00:00

    Hi Adin Mohhamed,

    To manually reclaim your unallocated ReFS volume space, you must launch an elevated PowerShell session and execute the command "Optimize-Volume -DriveLetter X -ReTrim -Verbose", substituting "X" with your target drive letter. For this manual operation to succeed, Windows must have delete notifications natively enabled at the OS level, which you can verify by running "fsutil behavior query DisableDeleteNotify" in the command prompt and ensuring the ReFS value is set to 0.

    Successful space reclamation also depends on your storage vendor configurations. Your SAN LUN must be deployed as a thin-provisioned disk, and the storage array controller must be explicitly configured to accept incoming UNMAP commands. Also, if your host server utilizes Multipath I/O to connect to the SAN, ensure your vendor's Device Specific Module drivers are fully updated, as outdated multipath configurations commonly drop storage reclamation commands as they traverse the fabric before they can reach the hardware pool.

    Hope this answer has brought you some useful information. If it did, please hit “accept answer”. Should you have any questions, feel free to leave a comment.

    VPHAN

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