It is exactly the same idea as the 2850: you cannot have a 1-disk RAID 1, and to use a single disk it must be a RAID 0. Also, if you do this using OpenManage, it is exactly the same as doing it on a 2850. If you are doing this in the CTRL-R utility, again, very similar - you create a new Virtual Disk, using the only available disk (the new one). Be sure to check the Advanced/Initialize boxes when creating it.   To be honest, I can't think how you possibly did this. It is pretty straightforward, and like I said, nearly identical to a 2850 - if not the exact steps, then the process. 
Hello everyone, hope you're all good. Today i've tried to add a new hard drive to my Dell poweredge 2950 as raid 1 bsides the other hard drive in raid 0, and i have totally forgotten how to separate two hard drives on PE 2950 because i deal a lot with PE 2850. Would you please give instructions.  Thank you in advance.
Raid configuration of raid 0 and raid 1 separately