Well, I tried to do a similar sort of thing and wound up loosing *all* the data in my /home directory. I had a single 2Gb ide as /boot, / and swap and two 40Gb IDEs in linear mode as /home.
I had to do a reinstall and thought to myself 'Ah, now worries, I'll just reinstall to the 2Gb drive and then remount the old /home once the install had finished.'
*BAD MOVE*
The e-smith installer, in it's infinite wisdom, decided that as I had 3 drives in my system it would put /boot on the 2Gb drive, swap on the first 40Gb drive and / on the 2nd 40Gb drive. The damn thing didn't even ask me or give me a clue what it was doing

Why are hdd's so much cheaper than decent tape drives these days?
Sooooo.....to do an upgrade or reinstall without loosing data I'd recommend disconnecting the two 100Gb drives you have and doing a standard upgrade to the system on the 2 SCSI discs, then remount the IDE raid after you've finished.
You'll also probably have to copy the bits and pieces out of /home back to the original /home on / to be able to perform the upgrade, but so long as you take everything but /home/files that shouldn't be too much.
Although you might just save yourself a lot of time and effort by just buying a new hdd...
Hope this helps...
Gary