Hi There,
If are runnnig a 2.6 kernel, you can perform the following that will scan all channels, targets, and LUNs on host H.
echo “- - -” > /sys/class/scsi_host/hostH/scan
Otherwise, I would reboot the server.
For adding new disk to volume groups, I trust you are using LVM
For an LVM howto consult the following link
http://tldp.org/HOWTO/LVM-HOWTO/
HTH
Steve