On A Quest For Better USB 3.0 Performance
Depending on controllers, devices, and hosts, USB 3.0 performance varies widely, and those jumps up and down are made evident in our benchmarks. And it's worth the research to figure out which combination of components is going to yield the best experience.
Turbo mode and UAS are both attractive technologies able to bolster the default behavior of USB 3.0. But they both require you connect devices that let the interface shine, meaning you need storage that won't gum up performance as a bottleneck. Hook up an external hard drive via USB 3.0, and it's going to deliver the same speed in pretty much every situation. Really, it takes some form of solid-state storage to make a difference.
And don't cross your fingers for better random I/O performance, either. Although we have to imagine that the number of folks leaning on USB-attached storage for workloads pushing heavy random accesses, it's worth mentioning that Turbo mode and UAS don't help. Really, sequential access patters stand to gain the most from both technologies.
Perhaps oddly enough, we saw the biggest gains from Turbo mode using the USB 3.0 devices that delivered the worst performance. Apricorn's SATA-USB 3.0 Adapter is a favorite lab tool, but it employs a poorly optimized USB 3.0 controller. A lot of inexpensive USB 3.0 enclosures and thumb drives fall into this category, and they're the ones that benefit most from Turbo—good news, since Turbo mode is basically free.
Enabling Turbo mode is a fruitless endeavor when you're using higher-end USB 3.0 devices, though, like Thermaltake's BlacX 5G, because its normal (BOT) performance is so good. UAS is the game-changer in this particular scenario; its sequential performance is as much as 20% higher, depending on your setup.
UAS is a fairly new technology, and so we're withholding judgement on it for now. Some of the vendors we contacted report much higher numbers than the ones reported here in their own labs, and we have every reason to believe higher speeds are possible. According to several of the engineers we contacted, development hardware achieves sequential speeds as high as 430 MB/s and random I/O exceeds 100 MB/s. In comparison, we hit 350 and 70 MB/s in both metrics, respectively, with our shipping hardware.
At the end of the day, UAS still offers tremendous potential, though PC enthusiasts might not even be the primary beneficiaries of it. As one Western Digital engineer pointed out, this technology is a real boon in the mobile and low-end desktop spaces. USB imposes a significant processing overhead using BOT, which helps explain why USB 2.0 and 3.0 often shows so poorly on older machines. The UAS protocol is more efficiently streamlined, creating less work for the host CPU. The addition of command queuing support opens the door to better performance because storage operations are processed in parallel. This combination of lower signal overhead and more efficient data transfers helps boost performance on older and cheaper computer systems, freeing the processor for other tasks.