Inside open manage / storage there are tools there to make changes to your array(s). Some co-workers of mine have expanded existing drives using this or the older array manager. I'd put the 3 disks in without adding them to the array in the bios and just let the server boot into the OS. Then try openmage and see if you're able to attach the new disks. I've seen the option there to expand the array, but never had an extra disk to see how it works through the OS.

Yes, I know how to add the disks to the array in openmanage server administrator and have them initialized. After that and a reboot, I can see in disk management that there is now unallocated space. What I am talking about is extending volumes and/or partitions (D drive in this case, which is the extended partition) to fill that space entirely. Diskpart can do it, but I am unclear on whether it works on extended partitions or not. I have seen microsoft links, one says it does, the other says it doesnt. I am also unclear on whether one has to extend a partition before extending a volume ...

Check out diskpart. For information how to use it, check the Microsoft support site.

Diskpart can extend basic volumes (there are a few limitations which the MS KB article explains).

Sorry, I meant ExtPart, not diskpart.