USB 3.1 Performance Preview: ASUS Z97-A/USB 3.1 motherboard

Next-Generation USB

In early 2013, we heard murmurings of an update to USB 3.0 that would double data transfer rates while remaining fully backward compatible with existing USB connectors and cables. Later that same year, the USB 3.0 Promoter Group announced the completion of the new USB 3.1 specification with the following features:

• 10Gbps USB data rate
• Compatibility with existing cables and connectors
• Improved data encoding for more efficient data transfer resulting in higher throughout and improved I/O power efficiency
• Compatible with existing USB 3.0 software stacks and device class protocols
• Compatible with both existing 5Gbps hubs and devices, as well as USB 2.0 products

With data transfer speeds of up to 5Gbps, USB 3.0’s SuperSpeed specification provided a significant speed boost over the 480Mbps on the older USB 2.0 standard. USB 3.1 has now managed to double this - its enhanced 10Gbps data transfer rates have been dubbed as SuperSpeed+, which translates into a theoretical peak rate of around 1.3GB/s as compared to 640MB/s for USB 3.0. Even though real-world numbers will probably fall short of these figures, we simply can’t wait to see wider adoption of the standard.

However, as with USB 3.0, mainstream adoption of USB 3.1 is likely to take quite some time and we’re likely to first see the standard make its way onto desktops first via add-on PCIe cards or third-party controllers before we start seeing wider implementation on mobile devices and drives. A case in point – ASUS has now moved to implement USB 3.1 functionality on its new motherboards, complete with add-on cards and support for existing Z97, X99 and B85 boards with updated BIOS. We’ll have a quick look at the major improvements in the USB 3.1 standard before diving into some performance figures for the new interface.

A detailed look at the USB 3.1 standard (SuperSpeed+)

The architecture of SuperSpeed+ USB’s communication layers is actually similar to that of USB 3.0’s SuperSpeed, but it features changes to the link layer, protocol layer, and physical layer for both the host and device. 

One of the more significant enhancements includes changes to the data encoding in the physical layer for USB 3.1 for more efficient data transfer and consequently higher throughputs. The physical layer consists of the PHY portion of a port and the physical connection between two ports. In order to signify the backward compatibility with USB 3.0, Gen X or Enhanced SuperSpeed system is used to designate a device/host combination that is capable of operating in both Gen 1 and Gen 2 mode.

USB 3.0 used what is called 8b/10b encoding (Gen 1), where transmitters in the physical layer scrambles and encodes 8-bit data into 10-bit symbols for transmission over the physical connection and a 5Gbps PHY signal. On the other hand, USB 3.1 switches to a more efficient 128b/132b scheme (Gen 2), where the new transmitter frames 128-bit data and control bytes by prepending a 4-bit header to differentiate between data and control. The move from 8b/10b to 128b/132b encoding thus reduces the bandwidth overhead from 20% to just 3% and improves data transmission efficiency from 80% to 97%.

In addition, because USB 3.1 was intended to not require any changes at the software level, it is compatible with existing USB 3.0 software stacks and device class protocols to facilitate use with existing host drivers. Many of the enhancements are thus found on the hardware level instead. For instance, USB 3.1 calls for new SuperSpeed Plus host controllers -- like the ASMedia ASM1142 controller on the ASUS boards – that will be able to utilize the additional bandwidth without requiring changes to existing host drivers.

But faster speeds aren’t all that are new with USB 3.1. The new standrad is also shepherding the adoption of the new USB Type-C port, a smaller, slimmer and reversible design that will fit into its corresponding female Type-C connector regardless of its orientation – great news for anyone who’s taken more than three tries to get their USB device plugged in. Incidentally, ASUS will be offering a single port USB Type-C card that can be purchased separately. Of course, USB Type-C is not backward compatible with existing Type-A USB ports, but passive adapters – such as this one from Apple – are available for newer Type-C plugs to interface with older USB 3.0/2.0 Type-A ports. However, users hoping to utilize the enhanced transfer rates of USB 3.1 will still need native USB 3.1 on both ends.

Test Setup

As mentioned before, ASUS’ USB 3.1 motherboard line-up includes both integrated USB 3.1 ports and PCIe expansion cards with the new connectors - boards designated as "/USB 3.1" will feature onboard USB 3.1 ports but those with the "/U3.1" suffix will come with an add-on PCIe 2.0 x2 card. Both solutions will be equipped with dual Type-A connectors - colored teal blue for easy identification - for better compatibility with a wider range of old and new systems. 

We will be testing the speeds of USB 3.1 with the ASUS Z97-A/USB 3.1 motherboard, which features four USB 3.0 ports and two teal-colored Type-A USB 3.1 ports on the rear I/O:-

ASUS has also supplied an external USB 3.1 Enclosure featuring two 250GB Samsung 840 EVO mSATA SSDs configured in RAID 0 for benchmarking purposes. The ASUS Enclosure sports a USB Type-C connector for data transfer and a microUSB port for power – both connectors need to be hooked up to the board in order for the drive to work.

On top of it all, ASUS has also introduced a new USB 3.1 Boost utility as part of its AI Suite 3 that features a Turbo mode primarily intended to improve performance on Windows 7. We’ll see how this all pans out as we explore our benchmark figures in the Results section.

We ran the tests on the following setup:

• Intel Core i7-4790K
• ASUS Z97-A/USB 3.1
• 2 x 4GB DDR3-2133 CL9 Crucial Ballistix RAM (1600MHz @ 9-9-9-27)
• Windows 7 Ultimate 64-bit

We had to make a couple of changes to the BIOS settings before running our tests. As per ASUS’ instructions, we disabled CPU C-States and Enhanced Intel SpeedStep Technology (EIST) before booting to Windows, after which we selected High Performance under Power Options.

Both CPU C-States and EIST serve to lower power consumption by optimizing the CPU operational frequency and voltage or allowing it to enter an idle state according to the demands placed on the CPU. But because the transfer of data is calculated through the CPU, this could affect the data transfer rate if transfer load ramps up while the CPU is idle. As a result, by changing the settings to ensure that the CPU is active at all times, we ensure that it is ready to handle data transfers at all times for the best performance. This also eliminates the resource overhead that results from the CPU constantly cycling between its idle and active states.

Of course, most users in real life enable these power saving features by default, so we've also penned down results observed when keeping BIOS settings as-is without tweaking it for the optimal scenario.

CrystalDiskMark 3.0.1 Results

CrystalDiskMark is a benchmarking utility designed to quickly gauge the performance of a storage drive. It measures sequential read and write speeds and random 512KB, 4KB, 4KB (queue depth = 32) read and write speeds.

USB 3.1 paired with ASUS USB 3.1 Boost (Turbo mode) was the clear winner here. It resulted in around a 35% increase in sequential read speeds a 32% increase in sequential write speeds as compared to USB 3.1 with Normal mode enabled in the USB 3.1 Boost utility. However, this lead narrowed and even fell away when it came to the random 512K and 4K read/write tests.

Given that everyday users are not likely to disable CPU C-States and EIST, we also ran these tests with the power savings settings in BIOS enabled to get an idea of the performance difference. What we got were sequential read/write numbers in the range of 455MB/s for USB 3.1 (Normal mode) and 670MB/s for Turbo mode, so users who run their boards straight out of the box without tweaking the settings can expect figures in this range.

AS SSD 1.7.4739 Results

AS SSD is a sequential benchmark that utilizes incompressible data for its tests. The results here mirror what we saw in CrystalDiskMark, where USB 3.1 (Turbo mode) posted sequential read/write transfer speeds over 750MB/s, only to have the lead narrowed down when it came to random read/write tests. The performance benefit of ASUS USB 3.1 Boost also disappeared when it came to performance in handling 64 files in parallel in the 4K read/write (64 Threads) test.

According to ASUS, its USB 3.1 Boost utility does not have the luxury of command queuing either as it relies on the ageing Bulk-Only Transfer (BOT) architecture, which can only handle one request at a time while waiting for the device handshake to complete before commencing with the next data transfer. As a result, it probably will not result in improved transfer performance for the simultaneous transfer of multiple files, which explains the lack of a significant difference between the transfer speeds of USB 3.1 in both Turbo and Normal mode in random read/write tests.

However, there is still an approximately 45% difference between USB 3.1 (Normal mode) and USB 3.0 in the 4K write (64 Threads) benchmark (as opposed to the 40% difference using USB 3.1 in Turbo mode), which can probably be attributed to the adoption of the SCSI protocol in USB 3.1. SCSI provides better data throughput than BOT because of its streaming architecture and better queuing and task management, which eliminates much of the round trip between command phases. The architecture is also better at multi-tasking, which further improves performance in instances where there are multiple transfers.

PCMark 8 Results

The PCMark 8 Storage benchmark is used to test drive performance with popular games and various editing and productivity software. Unlike synthetic storage tests, it is used as a gauge of real-world performance.

There is little difference between USB 3.0 and 3.1 here. We figure the insignificant difference is because of the mSATA drives and their controllers being the bottleneck, even though they are operating in RAID mode.

Then again, you’re more likely to be running these programs off an OS or onboard drive as opposed to a USB-attached device, although we do see USB 3.1 (Turbo mode) marginally inching out the other two in the overall scores and individual tests.

File Transfer Results

Lastly, we measured the time it took to transfer a 15GB batch of files from desktop to the ASUS USB 3.1 Enclosure. As expected, USB 3.1 (Turbo mode) was the best performer here, although it’s worth noting that it was only 3 seconds faster than when the Boost utility was set to Normal mode. On the other hand, USB 3.0 took 75 seconds to complete the transfer, which was a good 15 seconds slower than USB 3.1 with the Boost software disabled. Clearly, the improved data rate of the USB 3.1 standard is coming into play here.

We again ran the test with the power savings options in BIOS enabled to see the effect of this in real-world numbers as opposed to a synthetic test. We were glad to find that the difference is not that significant, with a timing of 63s for USB 3.1 (Normal mode) and 61s for Turbo mode. As most of the usage scenarios involving the USB interface center around bulk data transfers as in this test, everyday users probably don’t have to worry about going into BIOS to tweak the settings just to shave off that few seconds.

Preliminary Conclusion

USB 3.1 delivered fairly impressive figures in the sequential read/write tests, with transfer speeds almost doubling over USB 3.0 when Turbo mode was enabled. ASUS USB 3.1 Boost utility essentially had the greatest performance improvement in the latter tests as compared to random read/write tests and PCMark 8. Given that users using USB-attached storage devices in day-to-day use will probably find themselves dealing with sequential workloads more often, ASUS has focused on the right area to optimize with its USB 3.1 Boost utility.

In our real-world 15GB file transfer test, USB 3.1 (both Turbo and Normal mode) capably demonstrated that it was quite a bit faster than USB 3.0, so users who routinely transfer large videos, music and image files over USB can indeed look forward to speedier transfers.

In addition, ASUS has said that its USB 3.1 Boost utility is designed to show the largest performance on Windows 7 as the drivers for Windows 8.1 are already optimized for better performance with USB 3.1. As a result, users on Windows 8.1 can expect to see performance numbers that are similar to what we found for USB 3.1 with Turbo mode enabled on our Windows 7 test setup. Windows 8.1 users will be able to use the USB 3.1 Boost utility if they wish, but they will see a less significant performance improvement, probably in the range of 3-5%.

However, we must add that our test drives on the external enclosure were still stuck on the 6Gbps mSATA interface and at the end of the day, we're really not seeing the full potential of USB 3.1. This is the reason why we found some test results (such as PCMark 8) not bearing as much performance delta as we had hoped to see between USB 3.0 and USB 3.1 (Normal and Turbo). 

With that said, mainstream adoption of USB 3.1 is still likely to take some time as we wait for native ports on chipmakers’ chipsets, native OS drivers and additional accessories that utilize the new standard. But with what we’ve seen so far, we’re definitely looking forward to wider support for USB 3.1 in the coming months and we can't wait to test drive more suitable test products to really showcase the capabilities of USB 3.1.

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