One of the drives in my DNS-323 failed (Raid 1)

. How do I safely recover from this failure?
I had two identical 750 Gig Seagate configured as Raid 1 in the unit, one of the drives has failed, I just bought another identical drive to replace it, but what is the right procedure to do it w/o losing any data?
If I just replace the bad drive, does the unit automatically re-mirror the new drive from the working one?
Will I be prompted to re-format and/or reconfigure the unit as RAID 1 again?
I just don't want to loss any data and want to make sure I follow the right procedure.
Can I start the unit with just the one good drive and copy my data before doing anything else first? how?
Please HELP.
THanks.
RB