Several weeks ago when Apple released the first Thunderbolt-equipped Mac, the questions started pouring in on how quickly we’d be able to see the benefits of blazing external speeds.
Interestingly enough, no thunderbolt cables were even available until earlier this week when Apple started offering the Promise Technology Pegasus R4 & R6 RAID solutions. Now that the cables were available – we had to get our hands on a few to start answering the questions we’ve received in detail.
The first question we aimed to tackle came from Jay:
“Could I use a new 2011 Macbook Pro in Target Disk Mode over Thunderbolt? Wouldn’t it act just like an external hard drive enclosure?”
Logically, sure! Target disk mode allows one Mac with FireWire (or now with Thunderbolt) to be used as an external hard disk connected to another computer.
We decided to go for the gusto in our first test and installed a 240GB OWC Mercury Extreme Pro 6G SSD into the Main bay of our 2011 Thunderbolt port equipped 13-inch MacBook Pro. When we attached that to our 2011 Thunderbolt port equipped 27″ iMac via Apple’s Thunderbolt Cable in Target Disk Mode, we were expecting to get blown away by the raw data transfer rate.
Finally an external interface that wouldn’t bottleneck the 6Gb/s performance threshold of the drive.
What we found, however, was a modest gain in performance.
The FireWire 800 interface theoretically transfers data up to 100MB/s. In real life, peak rates typically are just below 90MB/s. Using Target Disk Mode over FireWire 800, we averaged 40MB/s reads and 38MB/s writes which equates to about 40% of the full capability of the FireWire 800 interface – as is typical with either an SSD or a hard drive in this situation.
Clearly there is some overhead in supporting Target Disk Mode.
By our logic, we figured that since Thunderbolt has a theoretical maximum data transfer rate of 1250MB/s we expected to see about 40% of that speed, or 500MB/s (which our SSD itself is capable of internally – see benchmark below). Unfortunately that wasn’t the case.
Using Target Disk Mode with an SSD over Thunderbolt averaged 74MB/s reads and 49MB/s writes, which was only a mere 4-6% of the full throughput capability that the Thunderbolt interface should be capable of.
Unless something changes with Target Disk Mode it probably isn’t wise decision to spend $50 on a Thunderbolt cable expecting to get massive speed transfers between your Thunderbolt equipped machines. For now, a simple FireWire cable is your more cost-effective solution.
This is just the beginning of our testing and a brand new technology. We’re excited to see what Thunderbolt is going to bring as it develops further.