dumb question about RAID and FC1 Install

[redhat]

I am in the process of installing a new mail server.  I have 5 drives -
2 with RAID 1 and the other 3 RAID 5.  The R1 array was intended for the
OS and the R5 for the data.  When I went in to configure the drives on
the GUI installation process the automatic drive configuration utility
selected both RAIDs for install by default.  I deselected my R5 side and
went ahead with the install on the R1 drives.  Didn't really think too
much about it at the time but now I can see the RAID 5 under /dev/sdb
but it is like "unformatted space".  Do I need to go back and do a
reinstall and let the install program use both RAIDS for the install
procedure or is there something "post install" that I can do to activate
these drives and begin using it for data?  Any help appreciated.
thanks,
Doug