Also, as a point of note, You are using Red Hat Enterprise Linux 5 (with a minor version that you omitted). Linux is too general, so as to not confuse you, or others, or start a flame fest about which distribution is better, you may want to be more specific (Besides just posting in the Red Hat section).
Truth be told, Linux is on 2.6. That is the version of the kernel, which is, by all rights, what "Linux" is.
For most physical drives, I like to run the following command:
lvmdiskscan | grep -v ram
However, if the drives have not been detected for some reason (you may want to restart udevd) you could run the command at the end of Scott's informative list:
Quote:
for S in $(ls /sys/class/scsi_host); do
echo "- - -" > /sys/class/scsi_host/$S/scan
done