A logical unit number (LUN) is a unique identifier used to designate individual or collections of hard disk devices for address by a protocol associated with a SCSI, iSCSI, fibre channel (FC), or similar interface. A sub-LUN is a higher granularity designation of a LUN. Sub-LUN migration automates the process of moving data to optimum storage devices by, for example, detecting data that has a high access rate and temporarily moving it to faster storage. When requests for the data drop off, it is moved back to the disk location where the original copy is stored.
Figure 1 – A sub-LUN migration mechanism moves Dataset A2 to a higher performance Tier B.