[I]"Bob, are you referring to Storage Area Network?"[/I]
Yes.
[I]"Why not use directly connected (fast) drives instead?"[/I]
Assuming you could fit enough Serial Attached SCSI (SAS) drives and their controller inside the chassis and only one workstation would need access to them no reason not to. That's still quite expensive. The SAS v3 interface now supports 12Gbps. The fastest SAS drives are 2.5" and don't hold much data so you need a lot of them to store the terra bytes of data the high end 4K cameras create.
Can only confirm my present HP Z820's , working like a charm and editing being a pleasure. Vegas restricts the amount of cores in preferences and internal prefs amount of cores gets reset to default ( think only 16 cores ) after restart of vegas . Have already asked many times SCS why they restrict that number of cores and RAM in prefs , as if there are no customers with real workstations using their software. No answers , of course . But it helps getting things go way faster , as adobe after effects being very happy when seeing AND USING lots of cores and RAM . And those HPZ 820-840 systems are really good ( also adviced by Avid , Adobe ) , have the 820's a few years now .
> "Like you said, can Vegas utilize all the cores to actually produce smooth playback"
Yea, that is the million dollar question. When I'm watching the timeline stutter and my CPU's are at 30% and my GPU is at 25% I have to ask myself... why would I buy more hardware when Vegas doesn't seem to be able to use the hardware I already have? Nothing is maxed out... where is the bottleneck?
36 cores sounds great.... if you have 36 things to do at the same time. ;-)