Dell Precision 490 - migrating Win 7 install to Raid 1 array; no clue why it won't boot!

I've got an older Dell Precision 490 workstation with a pair of 3 Ghz Xeon processors and 8 gigs of ECC ram.  System was running Win 7 ultimate (64 bit) off a single 1 TB drive with no problems for several years.

Decided to upgrade to a pair of 2 TB drives in a RAID 1 configuration (mirror) using the on-board controller that came with the machine.  Got the raid built, and both the bios and the OS see the array.

Bios reports array is bootable.  OS sees the array as a valid drive, and allowed me to do a hot-backup of the boot partition to the array (using Drive Image XML) with no problems.  All files were successfully copied to the array.

I then used EaseUS Partition Master to make a clone of the 125 meg system reserve partition on the original boot drive, and put the copy on the raid array in the 129 megs of unallocated space I left specifically for this.  Once the cloning was complete, I set that cloned partition to be hidden just like the one on the original OS boot drive.

So at this point I should be ready to disconnect the 1TB drive and allow the system to boot off the raid array, right?  Well, that's where I'm stuck.  No matter what I try, I can't get the system to boot from the raid array, despite the fact that it's at the top of the boot list in the bios, the raid config is set to "raid on" in the bios, and during POST the raid controller lists the drives in the array and states they are all OK and that the array is bootable.  After all that, then the system fails, saying that no bootable device was found.

ARGH!  Does anyone have a suggestion as to what I'm doing wrong here?