Microsoft Virtualization Discussions

Space Reclamation not working



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.








Re: Space Reclamation not working


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.


Hope this helps 🙏 

Jonathan Colón | Blog | Linkedin

View solution in original post

Re: Space Reclamation not working


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.



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