How to make my My Book Duo Raid 1 on a mac

Hi, wondered if you could help me please.  I have just bought a WD My Book Duo and have formatted it for MAC. It says it comes as RAID 0 and  I can’t work out how to Set it to RAID 1 so it’s mirrored.  I went into Disk Utility into the RAID section but I am a bit lost as to what to do.  It says Format MAC OS Extended Journaled and underneath RAID type Mirrored RAID set.  When I check on the hard drive capacity though through Get Info it still says 4TB so I am not sure if it is set properly.

Any help would be great thanks

All sorted, I didn’t realise I had to download WD Utilities