Thunderbolt: What you need to know

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More Thunderbolt speed results

Thunderbolt is quite fast, as our lab has experienced first hand. In our ongoing look at Thunderbolt performance, we tested two more configurations, as requested by Macworld readers. The first involves the new Promise Pegasus R6 Thunderbolt array configured as a RAID 0; the second is with Target Disk Mode using Thunderbolt. (Previously, we compared Thunderbolt and FireWire 800 speed. We also looked at Thunderbolt and eSATA.)

RAID 0 vs. RAID 5

When we first looked at how Thunderbolt performance compares to FireWire 800, we used a new Promise Pegasus R6 Thunderbolt array configured as a RAID 5. The results were impressive, but readers wanted to know what the performance would be like if the Pegasus R6 was configured as a RAID 0.

The Pegasus R6 is pre-formatted as a RAID 5 array, which offers speed as well as the security of knowing that any one drive in the array can fail and data will not be lost. RAID 0 (also known as a striped array) can be faster, especially when writing, but if any of the drives bite the dust, you lose all of your data.

The Pegasus R6 is Thunderbolt only, and we don’t have access to another six-drive array. So, as a point of reference with FireWire 800, we used the Promise SmartStor DS4600, a four-drive array. We reformatted the Pegasus R6 and the SmartStor DS4600 as RAID 0 arrays, connected them to our 15-inch 2.2GHz Core i7 MacBook Pro with a 250GB solid-state drive (SSD).

Promise Pegasus R6

In our AJA System Test, the Pegasus R6 RAID 0 write speeds were about 9 percent faster than the Pegasus R6’s RAID 5 write speeds. Read results showed the Pegasus R6 RAID 5 to be about 6.5 percent faster than the Pegasus R6 RAID 0.

Similarly, our 2GB file and 2GB folder tests on RAID 0 showed a bit of improvement when writing, and a bit of speed degradation when reading. The FireWire 800-connected SmartStor DS4600, on the other hand, was faster across the board when formatted as a RAID 0, though just by a megabyte or two per second in the read tests. Write tests were significantly faster in RAID 0 on the SmartStor DS4600, though still about half the speed of the Thunderbolt-equipped Pegasus R6 array.

Benchmarks: RAID 0 vs. RAID 5
Promise Pegasus R6 Thunderbolt

2GB File 2GB File 2GB Folder 2GB Folder
RAID 0 Read Write Read Write Read Write
Pegasus R6 Thunderbolt 510.1 710.2 178.6 215.6 133.5 161.8
SmartStor DS4600 FW800 83.6 77.3 85.7 77.7 73.8 70.6
Pegasus R6 Thunderbolt 543.2 650.3 183.5 210.5 143.9 160.1
SmartStor DS4600 FW800 82.9 56.5 83.2 47 72.5 50.1

All results are in megabytes per second (MBps). Higher results are better.

Target Disk Mode

Thunderbolt-equipped Macs support Target Disk Mode, when two Macs are connected via Thunderbolt (or FireWire) and one Mac acts as an external hard drive. We showed how to set up two Thunderbolt Macs in Target Disk Mode, and now we’ll take a look at the performance.

We connected a 17-inch MacBook Pro with a 256GB SSD and a 27-inch 2.7GHz Core i5 iMac via Thunderbolt. We ran the AJA System Test, with each Mac taking a turn as the target drive. We then repeated the tests over FireWire 800.

Benchmarks: Target Disk Mode via Thunderbolt

AJA System
AJA System
Read Write
17-inch 2.2GHz Core i7 MacBook Pro with SSD 205 179
—attached as external drive to iMac via Thunderbolt 58.3 39.6
—attached as external drive to iMac via FireWire 800 39.6 37.3
27-inch 2.7GHz Core i5 with1TB hard drive 115 116.1
—attached as external drive to MacBook Pro via Thunderbolt 48.7 29.6
—attached as external drive to MacBook Pro via FireWire 800 38.5 36.6

All results are in megabytes per second (MBps). Higher results are better.

When looking at the results, it’s easy to notice that the MacBook Pro’s SSD is much faster than the iMac’s 1TB hard drive. But what may not be so obvious is that neither connection is anywhere near as fast in Target Disk Mode as they are when acting as the boot drive. Also striking is that the performance differences between FireWire 800 and Thunderbolt in Target Disk Mode are so subtle. Target Disk Mode is a great convenience for transferring files and cloning systems, but it doesn't appear to be tuned for performance.

If you have a suggestion for a Thunderbolt test, please post it in the comments section below.

[James Galbraith is Macworld’s lab director.]

At a Glance
  • Promise Technology Pegasus R6 with Thunderbolt

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