Configuring RAID 1 mirroring

I have an uncertainty about configuring my 2 400GB drives in RAID 1. I currently am using 1 of them for storage and it does not have a backup. I have decided to purchase a 2nd drive and wish to set it up to mirror my current one.

My question is, will I lose the data on my current drive when configuring the RAID setup? I am just using the ASUS utility as the RAID controller is built into the board. So, should I find a way to backup before creating the RAID?

Thanks…