We recently outgrew the capacity of our 250 GB Hot Swappable hard drives on our Dell PowerEdge server in a RAID mirror. To increase capacity we took the 2nd 250 GB hard drive out of the second bay and popped in one of the new 1 TB ones. Using Dell's OpenManage software, we were able to automatically bring over an image of the 250 GB HD onto the new 1 TB. Everything seemed good there. After that completed, we were able to take out the other 250 GB Hot Swappable Drive and again use the Open Manage software to bring over an image of the new 1 TB Hard Drive from the second bay to the new 1 TB hard drive in the first bay. Everything still seems to be going smoothly and we were able to sell all of the data from our old 250 GB HDs and even save to the new drives. However, it only recognized 250 GB of capacity and not the full 1TB. We followed all of the steps from knowledgebase articles including using diskpart.exe to extend the drive but this would not work because we were in a RAID mirror. Of course we tried EASEUS software but it is possible that since that last 750 GB is not formatted because we just brought over an image of the 250 GB drive that it isn't recognized by EASEUS as well? Thus, we can't extend our C or D partitions into the remaining 750 GB of space. I'm sure people have encountred this before.

As of right now, we are looking into downloading a new BIOS which is probably 3+ years old and may not recognize the 1 TB hard drives?

Your array is only configured as 250GB mirror no matter what size physical drives you put it on.  The easiest solution is to image the current 250GB array, create a new 1TB array, restore the image, then expand the logical partition (using diskpart or some other utility).