topic Windows LUN space reclamation - space-allocation - not freeing blocks in ONTAP Discussions

Windows LUN space reclamation - space-allocation - not freeing blocks

pedro_rocha — Wed, 04 Jun 2025 09:55:33 GMT

Hello,

Environment is:

Windows Server 2016, ONTAP 9.5, LUN is thin, NTFS formatted, space-allocation WAS NOT enabled

On the host side LUN is 70% occupied, on the storage side, it is 100% full. On Windows, DisableDeleteNotify = 0

After reading several KBs, I am still in doubt. Some say you cannot enable space-allocation with the LUN online, some say you need to reboot the server after enabling it, some say you can enable space-allocation and just run a rescan on the host side.

Fact is that after enabling it with the LUN online and running a rescan, blocks are still provisioned on the storage side. I tried to create a new file inside the LUN and then delete it (there's a KB stating that this could trigger the UNMAP process). No luck.

Does anyone know the correct procedure?

Regards,

Pedro

Re: Windows LUN space reclamation - space-allocation - not freeing blocks

Ontapforrum — Fri, 18 Nov 2022 13:29:45 GMT

Please check this: (You might be hitting this bug, as you mentioned 9.5)
https://mysupport.netapp.com/site/bugs-online/product/ONTAP/BURT/1227997

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

This bug is reported to be introduced in ONTAP 9.5. This bug is resolved in ONTAP 9.5P3+ and 9.6+

Re: Windows LUN space reclamation - space-allocation - not freeing blocks

pedro_rocha — Fri, 18 Nov 2022 13:42:34 GMT

Hi, I don't think it is this bug. I forgot to mention we are running 9.5P5 (which has that fixed).

Re: Windows LUN space reclamation - space-allocation - not freeing blocks

Ontapforrum — Fri, 18 Nov 2022 14:49:12 GMT

Just going by the official NetApp documentation (Not kbs), it does clearly state: You must take the LUN offline to enable space allocation. I think if you just follow the 5 steps in the doc below, it should work.

Enable space allocation for SCSI thinly provisioned LUNs:
https://docs.netapp.com/us-en/ontap/san-admin/enable-space-allocation-scsi-thin-provisioned-luns-task.html

Re: Windows LUN space reclamation - space-allocation - not freeing blocks

pedro_rocha — Fri, 18 Nov 2022 14:57:01 GMT

Yes... I saw that and you are probably correct.

But than I saw thus: https://kb.netapp.com/Advice_and_Troubleshooting/Data_Storage_Software/ONTAP_OS/Storage_auto-reclamation_does_not_occur

"It is recommended to take the LUN offline to enable space allocation but for modern Host OS this is not strictly necessary if a rescan of the SCSI device updates as thin provisioned."

We'll try taking the LUN offline...

Re: Windows LUN space reclamation - space-allocation - not freeing blocks

Ontapforrum — Fri, 18 Nov 2022 15:42:27 GMT

Yes, go ahead.

I read that line - Modern OS, it is confusing, and I wonder which OS , further even if the Host is re-sending the scsi_inquiry (as part of the scsi_bus_scan) it is still picking up "old" data from the storage. Therefore, LUN must be taken offline so that the "SCSI inquiry" data on both nodes in the HA pair is updated.

Re: Windows LUN space reclamation - space-allocation - not freeing blocks

pedro_rocha — Tue, 22 Nov 2022 13:14:13 GMT

We have done all... offline/online the LUN, rebooted the server. No changes...

I have a opened case, we'll see what support says

Re: Windows LUN space reclamation - space-allocation - not freeing blocks

Ontapforrum — Tue, 22 Nov 2022 18:14:12 GMT

Sure, do let us know how it turns out.

In the meantime, could you share screenshot/output of the storage side space consumption and on the NTFS side.