SnapDrive uses the LUN clone split (rapid LUN restore) feature of Data ONTAP when restoring a LUN.
A LUN clone is a point-in-time, writable copy of a LUN in a Snapshot copy. After the clone is created, all read/write operations are made on the clone and read/write operations are no longer made on the original LUN.
A LUN clone shares space with the original LUN in the backing Snapshot copy. The clone does not require additional disk space until changes are made to it. When Data ONTAP splits the clone from the backing Snapshot copy, Data ONTAP copies the data from the Snapshot copy, and copies the blocks from the original LUN, to the clone. After the splitting operation, the clone becomes a regular LUN, and the original LUN is deleted by Data ONTAP.