You may already know that Thunderbolt ports can support up to six daisy chained peripherals. Just for kicks and giggles, Macworld decided to test how many devices they could daisy chain together using the Mac Pro’s six Thunderbolt ports, four USB 3.0 ports, one HDMI port, two gigabit Ethernet ports, and a partridge in a pear tree port. (OK, maybe not the last one.)
Macworld named the test the “Mac Pro Daisy Chain Challenge” and was able to connect a total of 42 peripheral devices to the Mac Pro.
Macworld connected 36 drives (19 Thunderbolt, 15 USB, 2 FireWire 800) with a combined capacity of 100.63TB. They also connected two Thunderbolt docks (the Belkin Thunderbolt Express Dock and the CalDigit Thunderbolt Station), an Apple Thunderbolt Display, two Apple Cinema Displays, and one HP Z Display Z27. WHEW!
A dozen of the drives were powered directly via the cables connecting them to the Mac Pro, the remaining 24 required external power. The combined power draw when running a script that copied data from the Pro’s internal flash storage to the external drives was 865 Watts.
The Mac OS X Activity Monitor showed that there was a combined throughput of 3 Gbps. The rate slowed as the fastest drives, (OWC’s Mercury Helios), finished transferring data.
Macworld also found that the daisy chaining didn’t affect the performance of a single drive working alone. However, the location of the drive in the daisy chain did affect performance.
More details, and a full list of all the daisy chained devices can be found at Macworld.