RAID 1 cannot be more than 2 drives, how are they using 3? you sure its not a RAID 5? Find out first by going to step 2 first. Yes RAID 0 can be one disk(but why), RAID 1; 2, RAID 5; 3 to a bunch more than 3
heres a cool link -
1. Insert your drive into the carrier, insert into system
2. Right click My Computer > Manage, Expand to the Disk Management (Dell Array Manager)
3. Configure your new disk by clicking Add Virtual Disk, your new unassigned disk should appear, it will tell you what options you have, (RAID 0, RAID1, i.e.) Click OK
4. Expand to Disk Management (Windows) It should prompt to initialize disk and configure and format with a drive letter.
To reconfigure your arrays, press CTRL+M at boot to enter the array manager BIOS, and reconfigure the drives, BUT going from any array level to anything else will usually wipe out your data requiring a reinstall.