Add mirror greyed out ?

I recently installed windows server 2003 on an adaptec 29160 and there are currently 3 disks on the adapter. I converted all drives from basic to dynamic , including system and boot volumes. I am currently trying figure out why when right clicking on Disk 0, “add mirror” is not available and neither on Disk 1. The whole purpose of getting these 2 same size disks were to test out mirroring and now I dont even that option. Furthermore, if I right click on my 3rd drive which has two volumes , I do have the option to mirror. I don’t get it, I just want my system drive to mirror in case something happens to it. Any help would be great;y appreciated, Sincerely, Carlos