Mounting raid disk

[Sauro Cesaretti]

Hello Everyone, 

I'm helping a friend to build a nas using a normal desktop pc.
Now, the problem is that he has 3 disks.
1 that is configured as primary where we installed ubuntu and the others
are configured as raid and they are still not mounted.
First, How can I discover if ubuntu recognized the raid properly?
second, how can I mount this unit in fstab?
Thanks so much in advance for your support.
best regards, Sauro