RAID 5 Configuration for new disks

Hi, I want to replace the 2 crashed hard disks of external storage for Unix server which consists of:

Model: ALPHASERVER ES40
Operating System: Compaq TRU 64 unix v-5.1
Database: Oracle 8i
Raid 5 configured on the existing 5 disks.

My question is

Can i just replace the crashed disks with new ones, when the server is running. Will the system automatically configures these 2 new disks with raid 5 and everything will be same as previously.

Or do I need to configure raid 5 for these 2 new disks, if so how to do that. Kindly advise me in this regard.

thanks,