For Redhat 7.0 and up, you should not need to modify any initscripts to enable LVM at boot time if LVM is built into the kernel. If LVM is built as a module, it may be necessary to modify /etc/rc.d/rc.sysinit to load the LVM module by adding "modprobe lvm-mod" before the section that reads:
# LVM initialization, take 2 (it could be on top of RAID) 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 init script fragment is from Red Hat 7.3 - other versions of Redhat may look slightly different.
For versions of Redhat older than 7.0, it is necessary to edit the file /etc/rc.d/rc.sysinit. Look for the line that says "Mount all other filesystems" and insert the vgscan and vgchange commands just before it. You should be sure that your root file system is mounted read/write before you run the LVM commands.
You may also want to edit the the file /etc/rc.d/init.d/halt to deactivate the volume groups at shutdown. Insert the