SCSI UNMAP is the mechanism used by a supported SAN host to inform ONTAP that logical blocks within a thin-provisioned LUN are no longer required. Deleting files within Windows normally changes the filesystem ' s allocation information; without storage reclamation, ONTAP may still regard the associated LUN blocks as allocated. When LUN space allocation is enabled and the host supports logical block provisioning, Windows can issue SCSI UNMAP commands identifying unused blocks so ONTAP can return that physical capacity to the available storage pool. A SCSI reservation controls device-access coordination and does not reclaim capacity. Snapshot Autodelete manages Snapshot copies, while SnapCenter provides application-consistent data protection and management. Therefore, SCSI UNMAP is the SAN protocol operation responsible for reclaiming blocks released by the Windows filesystem.
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