I don't know if this will help but here follows the lists of modules
that are included in the initrd of two systems.

The first system, Duo1, has a SATA disk and does not use LVM --

[root@Duo1 ~]# gunzip < /boot/initrd-$(uname -r).img | cpio -it
2>/dev/null | grep ko$ | sort
lib/ahci.ko
lib/ehci-hcd.ko
lib/ext3.ko
lib/jbd.ko
lib/libahci.ko
lib/libata.ko
lib/ohci-hcd.ko
lib/scsi_mod.ko
lib/sd_mod.ko
lib/uhci-hcd.ko
[root@Duo1 ~]#

The second system, stxsl, has two EIDE (PATA) disks logically combined
together by LVM --

[root@stxsl ~]# gunzip < /boot/initrd-$(uname -r).img | cpio -it
2>/dev/null | grep ko$ | sort
lib/ata_generic.ko
lib/ata_piix.ko
lib/dm-log.ko
lib/dm-mirror.ko
lib/dm-mod.ko
lib/dm-region-hash.ko
lib/dm-snapshot.ko
lib/dm-zero.ko
lib/ehci-hcd.ko
lib/ext3.ko
lib/jbd.ko
lib/libata.ko
lib/ohci-hcd.ko
lib/pata_acpi.ko
lib/scsi_mod.ko
lib/sd_mod.ko
lib/uhci-hcd.ko
[root@stxsl ~]#

Notice the six dm- modules that are included as a result of using LVM?

Alan.