Exam NS0-163 topic 1 question 56 discussion

Enable space allocation to allow your hosts and storage systems to cooperate on LUN space management. ... A host can perform SCSI UNMAP (sometimes called TRIM) operations: These operations allows a host to identify blocks of data on a LUN that are no longer required because they no longer contain valid data. https://docs.netapp.com/us-en/ontap/san-admin/enable-space-allocation.html

D then B

I don't think vmfs unmap (option A) is correct. Vmfs unmap should only be needed on older datastores that don't support automatic space reclamation and if unmap was being used then none of the other three would be needed. I think this question is referring to the steps for enabling space allocation on thin provisioned LUNs, which include the command to enable it (option D) and rescanning the storage from the host (option B). https://docs.netapp.com/us-en/ontap/san-admin/enable-space-allocation-scsi-thin-provisioned-luns-task.html "The space-allocation option is set to disabled by default, and you must take the LUN offline to enable space allocation. After you enable space allocation, you must perform discovery on the host before the host will recognize that space allocation has been enabled."