UNMAP Capability Feature
The UNMAP capability feature is a SCSI command that is used with thin provisioned storage arrays. With thin provisioning, after data has been marked as deleted the space is still allocated by the storage array. Because the array is not aware that the data has been deleted, inefficient space usage occurs. The UNMAP feature allows an application or OS to tell the storage array that the disk blocks contain deleted data so the array can deallocate the blocks. This reduces the amount of space that is allocated or in use on the array. This function allows thin provisioning to clean-up after itself and greatly increases the value and effectiveness of thin provisioning.