I guess the first thing to point out (which may be obvious) is that the metadata representing the OS RAID-1 is different than the metadata representing the hardware RAID-1. This means that the information stored on the disk that says “these two disks are a mirrored pair” is different for OS and hardware RAID. Therefore you can’t move the RAID-1 from OS to hardware.
However you CAN break the OS mirror and then import one drive of each pair into the hardware controller as stand-alone drives. Then you would add the other two drives and tell the RAID card to convert the single drives into mirrored pairs by copying data from one drive to the other.
There is one potential issue. The hardware metadata uses some number of sectors on the disk. These sectors are hidden from the OS. You’d need to make sure that the resultant size of the disk after these sectors are allocated is still large enough to hold the original OS partition. Most partitions don’t use the entire drive, so you “may” have enough room on the disk for the hardware metadata. The controller GUI should properly warn you if you try to import a a drive that won’t be large enough for an existing partition. If that happens, then unfortunately you will have to backup and restore your data.
Hope that helps. These comments were meant to be generic enough that they “could” apply to any vendor’s RAID controller, not just an Adaptec RAID controller, but I can’t vouch for other vendor’s functionality.
P.S. As you probably noticed, I “assumed” that you were moving the currently mirrored drives to the hardware RAID controller. However if you’re just adding the new controller with new drives, then obviously ignore all that. 🙂 In which case, yes, you can add the new card and drivers without reformating and rebuilding the Domain Controller.