NetApp LUN space allocation setting

[Zulhadi]

Hi all,

I having an issue on space discrepancies between storage LUN and end host space (LUN that mapped on windows server). After go through some research, I found out that required to enable the space allocation on thin LUN to make host-side space management identifies blocks of data that have been deleted on the host file system allow ONTAP to reclaim space. I've already enable the setting for space allocation and just want to ask few asking here after we enable the feature.

1) After we enable the space allocation feature/setting in the LUNs and already verify the features is already enabled, how long can we can expect to see the reflect of space on the storage LUN will align/tally with the space available in the host end?

Please advise as I need to understand what the result we can expect after enabled the space allocation feature. Tahnks

[dbenadib]

Hi,

Did you unmount / mount the lun after changing the settings? That's a mandatory step for Windows to discover that SCSI Unmap has been enabled.

This option also enables Data ONTAP to reclaim space automatically  when your host deletes data.

Here is some interresting links about space-allocation parametter:

1- Set up

https://docs.netapp.com/us-en/ontap/san-admin/enable-space-allocation.html 

2 - KB Space auto reclamation does not occur

https://kb.netapp.com/on-prem/ontap/da/SAN/SAN-KBs/Storage_auto-reclamation_does_not_occur 

David BENADIBA

[Zulhadi]

Hi @dbenadib,

Thanks for your response. I'm not do unmount/mount the LUN after enable the space allocation but I do rescan the disk in the disk management (action > rescan disk) as I've read in the KB, we only need to rescan the disk.

Just want to ask you, if we enabled the space allocation in the LUN, would the LUN will automatically sync to same size as shown in the mapped LUN on end host server? Let say before activated the LUN space allocation, the size LUN used in the host end is 3TB but in the LUN in storage is used 4TB, will we expect after enable the space allocation, the size is LUN in storage will same as size the presented LUN mount in host end server which is 3GB? 

[dbenadib]

That should happen automatically when client sends UNMAP requests nevertheless you can enable statistics to check if your host is sending UNMAP requests:

You can validate that SCSI Unmap is enabled on your Windows host by doing the following:

• Run the command to verify setting from 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.

[Zulhadi]

Hi sir @dbenadib,

Thank for your response. Thanks for your response. I will check later the setting for verification.

About my second query, will the size in the storage LUN will follow exactly as same size as the mapped LUN in the storage end once the feature is enabled and after host is success sending UNMAP requests? Can you enlighten me on this if you have an idea on this? Thanks sir