I know how to do LUN rescan under Linux using echo command. A reboot option (downtime) is not available for me. How do I rescan LUN under Solaris UNIX operating systems?

The cfgadm command provides configuration administration operations on dynamically reconfigurable hardware resources. Pass the -l option to Lists the state and condition of attachment points specified. Login as root and type the following command:
cfgadm -al
For further information read cfgadm and format command man page