Thunderbolt: How devices affect each other on a daisy chain

By James Galbraith, Macworld |  Storage, Apple, Thunderbolt

We then attached all three storage devices to the MacBook Pro, with the Pegasus R6 first in the chain connected directly to the MacBook Pro. The LaCie SSD was second in the chain, and the LaCie hard drive was last. When we ran the AJA System Test again, the Pegasus R6 saw a slight performance improvement, with a write speed of 543.0MBps, and a read speed of 520.3MBps.

The LaCie SSD, second in the chain (attached to the Pegasus R6), scored about the same as it did when connected alone, with a write speed of 246.9MBps and a read speed of 469.4MBps. The LaCie hard drive, the last device on the chain (attached to the LaCie SSD), posted scores that were a touch faster than when attached alone: a write speed of 190.1MBps, and a read speed of 205.4MBps.

We then changed the order of the devices on the chain, placing the Pegasus R6 last on the chain, and the LaCie SSD first, with the LaCie hard drive in-between. The Pegasus R6 scores were just a touch slower, with a write speed of 532.8MBps, and a read speed of 513.2MBps. With the LaCie SSD connected to the MacBook Pro, it scored about the same as it did in the second position. The same was true for the LaCie hard drive.

Drives and a display in a daisy chain

In our next series of tests, we added an Apple Thunderbolt Display to the end of the chain. All of the drives turned in speeds very similar to the speeds they posted without the display. Swapping the Thunderbolt Display with an Apple 27-inch LED Cinema Display didn't change performance much, either.

With the Thunderbolt Display as the first device (and the only display) in the chain, the LaCie SSD experienced a small performance hit. There was no real performance change on the LaCie hard drive.

Daisy chain with two external displays, three drives

Things got interesting when we connected two Thunderbolt Displays to the end of the chain. Our results were similar to the results we saw in a report by AnandTech. Having multiple displays in a chain affects performance.

The LaCie SSD went from 249.7MBps (write) and 472MBps (read) with one Thunderbolt Display attached, to 153.9MBps (write) and 438.8MBps (read) with two Thunderbolt Displays on the chain. The LaCie hard drive's read performance was unaffected, but the write speed decreased from 183.9MBps to 159.4MBps.

The Pegasus R6 saw the most dramatic change, with its write speed dropping from 553.7MBps to 231.0MBps, and its read speed dropped from 527.4MBps to 420.7MBps.

Originally published on Macworld |  Click here to read the original story.
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