Dynamox is correct, but in "short":  LUN migration enables you to move a LUN to another location, whether this is on the same Raid Group (RG) or on another RG, that's up to you. You can migrate a LUN for example from a RG consisting of 146GB15k drives to another RG made out of 600GB15k drives, or even SATA if you like. You can also migrate a METALUN to a simple LUN.  It works as follows: Suppose you have LUN 10 that you'd want somewhere else in this Clariion (it only works internal, not between 2 or more Clariions) and this LUN is 100GB in size. It doesn't matter whther or not this is a simple LUN or a METALUN. Now you create an equally sized LUN where you want the LUN 10 to be. It doesn't matter what LUN number you create. Now you start the migration to that new empty LUN. When the migration is done the new LUN takes over the identity of the old source (META)LUN. Host I/O is never interrupted and the LUN wwn doesn't change, so it's nondisruptive !  This way you can easily migrate from RAID6 ro RAID10 !
Dears,   Can any one please explain what is LUN migration? when  it use?   Best regards, Muneer. 
LUN migration