Witness disk - LUN or Disk

Hi

Server 2012 R2

I am wanting to set up Failover clustering with 2 nodes connected to a Dell MD3400 storage array using SAS (not iSCSI).  The disks are a mix of SSD and SAS drives and  have been configured as 2 disk groups (LUN 0 for all the SSD drives and LUN 1 for all the SAS drives).

Reading up on 2 node Failover clusters suggests that a Witness disk is need for Quorum and this should be a "Dedicated LUN that stores a copy of the cluster database" (https://technet.microsoft.com/en-GB/library/jj612870.aspx).  Other resources suggest a Witness disk of 1GB.  My questions are:

1. Would the prefered location for the Witness disk be on the SSD or the SAS drives
2. Should I reconfigure my Storage to have a separate LUN for the Witness disk or would a 1GB 'drive' suffice?

Thanks
Tony