topic Re: Space Reclamation not working in Microsoft Virtualization Discussions

Space Reclamation not working

OmotayoZadok — Wed, 04 Jun 2025 10:21:01 GMT

Hi,

I provisioned thin-provisioned LUNs from my NetApp controller in Cluster mode to a Hyper-V server.

However, it seems like I can not reclaim space from this LUN on the storage end.

there is a command I can run on both ends to fix this anomaly if it were VMware. Is there a command I have to run on the storage end to fix this, or is it a bug with Microsoft Hyper-V?

LUN is thin-provisioned

Space reservation is enabled

Space allocation is enabled.

thanks.

Re: Space Reclamation not working

jcolonfzenpr — Mon, 21 Jun 2021 13:33:02 GMT

Follow the KB article:

How to verify whether SCSI UNMAP is enabled or disabled on a Windows host?

Run the following command to verify the setting from the command prompt:

> fsutil behavior query disabledeletenotify

The returned value (DisableDeleteNotify = 1) means in-band UNMAP is disabled for the host.

DisableDeleteNotify = 0 means in-band UNMAP is enabled for the host.

https://kb.netapp.com/Advice_and_Troubleshooting/Data_Storage_Software/ONTAP_OS/ONTAP_and_Windows_SCSI_unmap_and_space_reclamation

Hope this helps 🙏

Re: Space Reclamation not working

ChanceBingen — Tue, 22 Jun 2021 13:38:08 GMT

Just adding to the previous post, you also need to make sure that the space-allocation option is enabled on the LUN in ONTAP. This KB gives a little more detail: ONTAP and Windows SCSI unmap and space reclamation - NetApp Knowledge Base

One thing to highlight in the KB is that if you change the option on the LUN, you need to reboot Windows to see the change.