[CentOS] CentOS6: HELP! EFI boot fails after replacing disks...

OK, I wanted to replace the 500G disks in a Dell T20  server with new 2TB 
disks.  The machine has 4 SATA ports, one used for the optical disk and three 
for the hard drives.  It is set up with /dev/sda and /dev/sdb with each three 
partitions:

1 -- VFAT (for EFI)
2 -- ext4 (for /boot)
3 -- LVM

/dev/sda2 and /dev/sdb2 are a mirror raid (/dev/md0)
/dev/sda3 and /dev/sdb3 are a mirror raid (/dev/md1), with LVM on top of that.

/dev/sdc is a disk containing one file system and mostly used by AMANDA for 
backup (it has a "virtual" tape changer).

This morning I shut the machine down and pulled [the 500G] /dev/sdb and
installed a new 2TB disk as a new /dev/sdb. Partitioned it (with parted) to be
much like /dev/sda (except partition 3 is way bigger). I added the new
/dev/sdb2 to /dev/sda2 (boot raid set) and dd'ed /dev/sda1 to /dev/sdb1. I
then created a new RAID set (degraded) with /dev/sdb3, used pvcreate on it,
used vgextend to add it to the system volume group, then used pvmove to move
the extents from the old disk to the new disk. Meanwhile I partitioned a
second 2TB disk using a USB SATA dock and copied the old 500G /dev/sdc1 to the
new 2TB disk. So far so good.

Then I shut the machine down, swapped in the new backup [2TB] disk and pulled
the old system [500G] disk and installed the third new [2TB] disk. The system
won't boot that way. It seems there is something in the UEFI (secure boot)
logic that wants the original disk, even if everything is moved over.

I ended up putting the original /dev/sda in.  The machine boots and is using 
the new system disk (a raid array in degraded mode).

What is the magic to fix this?  

I tried to run efibootmgr, but it wants a model named efivars loaded, but 
there is no such module available.

What am I missing?

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