Witness Disk and Quorum Mode

Hi,

I have two node clusters of windows server 2008 R2 servers. Before configuring cluster I have created two shared disk (Disk1 512 MB Space and Disk2 1024 MB Space).While configuring Cluster Disk2 is automatically chosen as Witness Disk and Node&Disk Majority as Quorum Mode.

Is there any criteria to select witness disk automatically?  

Is it Possible to select quorum mode while configuring 2 node cluster

T/R

A