nMP Thunderbolt Bus Question

There are three Thunderbolt controllers int the Mac Pro 2013. In Apple's terminology they provision three Thunderbolt buses which are outlined here:


http://support.apple.com/kb/HT5918

In particular is the note there:

"... Note: Attach displays to different Thunderbolt busses when possible (see figure below). .. "

Each port on the Mac Pro can either be a Thunderbolt (TB) or mini DisplayPort (DP) port depending upon what is immediately plugged into it. (and possibly what is plugged into the HDMI for bus 0. Each bus only can support at most two displays. )

Given the number of TB devices to follow there isn't a good reason to put two of these displays onto the same TB bus. Similarly, unless some distance requirement, little good reason to not to directly connect these.

Directly connected this is DP bandwidth not TB bandwidth. You 'loose' an operational TB port, but you don't loose any TB bandwidth. Given have 6 TB ports ( 4 left ) it is a decent trade off to manage bandwidth.

Both of these tend to push data in one direction. TB is bidirectional so there is inboud and outbound ( relative from Mac Pro) bandwidth. Two major inbound devices on the same TB bus are going to compete with one another.

Devices that both read (inbound) and write (outbound) alot of data may need isolation. Similarly, devices that aren't concurrently used very often will share a bus direction better.

rather course grain you can use Activity Monitor to see disk activity. ( iostat is a command line tool to probe system storage activity ). If trying to probe low level PCI-e activity that TB encapsulates and transports it is more complicated ( Instruments). This page has a set of tools.

http://www.brendangregg.com/USEmethod/use-macosx.html


But first step would be looking into the TB devices support docs to see what they outline as being the bandwidth requirements/specs for representative loads.