You've added a scsi disk on a controller and you don't want to restart linux to scan the scsi bus ? Tell the kernel directly that a new scsi device was added .
The previous method was to use the echo command talking to /proc/scsi/scsi : For example , we've added a scsi disk on the first scsi controller (0), on the first channel (0), with a scsi id 4 (4) and on LUN 0 (0) : echo "scsi add-single-device 0 0 4 0" > /proc/scsi/scsi
Now (better and updated solution) : echo "- - -" > /sys/class/scsi_host/host0/scan
Check with cat /proc/scsi/scsi that you're able to see the device and use the disk without having to reboot ....