rc.sysinit contains the following code to initialize LVM volumes: 
 
 # LVM initialization 
 if [ -f /etc/lvmtab -a ! -e /proc/lvm ] ; then 
         modprobe lvm-mod >/dev/null 2>&1 
 fi 
 if [ -e /proc/lvm -a -x /sbin/vgchange -a -f /etc/lvmtab ]; then 
         action $"Setting up Logical Volume Management:" /sbin/vgscan && /sbin/vgchange -a y 
 fi 
 
This does _NOT_ work with LVM2's dm-mod which is included in latest RH kernels. 
 
I'm using this instead to activate LVM2 partitions: 
 
 modprobe dm-mod 
 if [ -x /sbin/vgchange -a -f /etc/lvmtab ]; then 
         action $"Setting up Logical Volume Management:" /sbin/vgscan && /sbin/vgchange -a y 
 fi 
 
 I don't know how to detect wether the modprobe is really needed on the booting system.