In the file /proc/scsi/scsi appears the devices.
In addition there are tools that permits a rescan units, for example for hp is hp_rescan. Also Qlogic and Mylex have their utilities.
QLogic FC HBA LUN Scan Utility
This utility scans for the newly added LUNs. After adding the new LUNs it is not required to unload/load the QLogic FC driver or reboot the system. To see the newly added LUNs, just run the ql-scan-lun.sh utility.
The simplest way to use this utility is to run