ml350 g5 extend array

Hello,

I have a ML350 G5 server with Smart array controller E200i (128 Mb). I have a RAID5 array with 4 HD sas 72Gb 3,5" (3 + 1 hot spare).

now, i have 2 free bays and i want to increse the archiving data space.

If I connect 2 HD same as the 4 installed, can I extend my existing array or i must create a new additional one, ex: a RAID1?

thank you!