I have 7 identical provisioned RH EL6 x86_64 virtual machines. All had to get a changed disk layout (requirement of the application owner which wasn't communicated before they started installing stuff). So I shut down each server, added another disk temporary, told the VM to start with the RH EL6 DVD and then ran the repair option.
Now I would format an ext4 file system on the temporary drive, use dump to backup the existing file systems, then modify the OS drive to the new partition layout, mkfs, restore, reinstall grub, etc. etc. Modified the UUID in grub.conf and fstab. Shutdown server, remove DVD and temporary drive. And power on again. Voila, application owner has the layout as needed.
This worked fine on 6 of 7 servers. But one of them will not the life of it load a SCSI driver now. I tried both the VMSCSI and LSI SAS, both lead to no drive found (neither by UUID and block(0,0)). A dump of the kernel messages indicates no driver is getting loaded at all. I tried to clone the machine, didn't help either.