I'm trying to fix a (very messy) system that the user hosed by running a kernel upgrade from 3.7.10 to 3.9.6. the root file system is on an LVM volume on top of a software RAID array. The boot manager is grub2.The 3.9 kernel is unable to mount the root file system. It spits out the usual not-very-helpful bit about the device node not existing. This happens whether I use the UUID, the /dev/{vg}/{lv} or /dev/mapper/{vg}-{lv} notation for the root file system in the grub config file.The 3.7 kernel on the other hand is still on the machine and actually mounts the root file system and boots up just fine. Unfortunatly the modules got removed so even the keyboard doesn't work. I can book it up to a rescue cd, in which case the RAID arrays and LVM volumns come up just fine.Both kernels have matching initrd files that include the same set of modules. The initrd file is created by genintrd as part of the post-install process of the package manager1. LVM is built in and MD modules are present in the initrd. Further inspection2 of the init file shows they have identical root fs paths, the same one grub is passing in.I have tried searching around for the net for related issues but none of the cases out there seem to quite match this. I was unable to find anything about changes in the 3.9 kernel that would necesssitate a configuration change on the system from 3.7. What changed to the handling of LVM root file systems in 3.9?1. The distro is PLD-Linux, an RPM based distro. Kernel packages are stock rpm's from the TH tree.2. Inspected each one by extracting it using gunzip | cpio -i and observing module and script files. 
What changed between kernels 3.7 and 3.9 that affects LVM/RAID root file systems?
linux kernel;software raid;kernel panic;lvm;root filesystem