Extending existing local datastore on stand alone ESXi Host

Hi,

Looking for some advice on adding disks / extending a single datastore.

We have HP DL380 G6 Server, running stand alone instance of ESXi 5.1, with local storage only.  RAID1 (2 x 146gb) for ESXi OS install, and RAID5 (4 x 300GB) which is presented as the Datastore where the VM's reside. There are physically two more empty bays, (bay7 & bay8), in the Server, and would like to populate with another 2 x 300gb disks and add to the RAID5 setup / expand the Datastore.  Has anyone any thoughts or suggestions on how to approach this?  The VM's will be backed up as precaution.

Thanks,