AiO 1200 - Newbie Qs

[desijat]

Hi - I just started working on a new AiO1200 (6TB). I created a test share and an iSCSI target (w2k3 server being the initiator). All is working well. However, when I look in the ACU on the AiO, I see that Array 1 has 2 LDs (I assume OS and DONT ERASE). Array 2 was created for the share, and I guess the iSCSI target. But why is there approx. 890GB unused in Array 1. Does this ever get allocated i.e. based on usage will this be assigned for other storage, as and when created/assigned?