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Lab tested: The Mac Pro Daisy Chain Challenge

James Galbraith | April 25, 2014
A Thunderbolt daisy chain can support six connected peripherals per port. And the Mac Pro has six Thundebolt ports, four more than any other Mac. The Mac Pro also has four USB 3.0 ports, one HDMI port, and two gigabit ethernet ports, so you can connect a lot of devices to one Mac Pro.

Looking at OS X's Activity Monitor during this operation, we saw overall throughput of around 3 GBps with all the drives running. As the faster drives finished the task, the overall rate slowed dramatically.

We also tested to see how having all of these drives connected might affect performance of a single device. We took the Promise Pegasus R6 and ran four different read/write tests, with the R6 in different locations in a daisy chain. When located at the beginning of a six-device chain, with all the drives attached, the R6 posted an average write speed of 709.8 MBps and read speed of 584.7 MBps. Moving the R6 to the end of that chain with all other drives still attached, the average write speed dipped to 556.7 MBps while read speeds were pretty much unchanged at 591.5 MBps. Repeating that test with only the Pegasus2's chain attached did not affect performance at all.

Finally, we connected the R6 directly to the Mac Pro with no other drives attached. Those results were nearly identical to the first test, with the R6 at the beginning of the chain and the other drives mounted on the desktop. In this case, placement in the chain is more important than the presence of other devices.

Have some tests you'd like to see run? Let us know in the comments.

 

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