About Add volumes Question?

[hartball38]

Hi .
I use FreeNas 8.
And I Want to create a new Volumn.
As the page : http://doc.freenas.org/index.php/Volumes
i can see the "Member disks" ,
But i my server ,the step of carate volumns ,I can see any Disk.
where the disks come form?
Can't I create a disk by useing FreeNas 8?

Can't I split the space form the freenas space,and create the space to be a new Volumn.
Or, I need a hpysical disk as a member disk?

thx