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Thunderbolt's Bandwidth: Sizing Up To USB 3.0, FireWire, And eSATA

Everything You Need To Know About Thunderbolt
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Thunderbolt was designed with a number of usage models in mind, one of which is high-bandwidth, low-latency data transfer for audio and video professionals. That has sequential transfers written all over it. And so, we're able to fire up Iometer and cram as many 128 KB blocks through the interface as possible in order to gauge Thunderbolt's potential performance.

In our quest to test the limits of external storage interfaces, we rounded-up a handful of external RAID enclosures (subsequently disabling caching).

We got our hands on LaCie's 4big Quadra to use with FireWire 400/800, USB 2.0, and eSATA. It was a little harder to track down a USB 3.0-capable solution, but we managed to snag a DriveStation Quad USB 3.0 from Buffalo Technology. Promise sent us its Pegasus R6 with Thunderbolt compatibility. All enclosures were loaded up with Hitachi DeskStar 7K3000 drives.

Thunderbolt wins hands-down in a raw performance comparison, with the hard drive-based Pegasus R6 maxing out at up to ~925 MB/s at high queue depths. Because the cable's second Thunderbolt channel is used for display data, that ~925 MB/s figure is very close to the interface's 1 GB/s theoretical ceiling in one direction. Despite that ceiling getting hit, Thunderbolt simply destroys the other five interface options.

Notice in that chart above that there are lines for hard drives and lines for SSDs. Crucial lent us six m4 SSDs, just in case the hard drives failed to saturate our connections. What we saw, though, was that the DriveStation Quad and 4big Quadra didn't speed up after replacing disks with SSDs. Throughput from the Pegasus R6 did increase to 965 MB/s, though.

This small performance delta confirms that we're saturating the Thunderbolt interface with six hard drives in RAID 0. With four disks (Pegasus R4), performance tops out at 600 MB/s using Thunderbolt. We also see that the SSD-equipped Pegasus R6 achieves better performance at lower queue depths than the version with hard drives.

The above chart represents peak throughput from our sequential results, derived from testing a single device attached to a Thunderbolt port. According to Promise, as you add devices, aggregate performance slowly starts to slide due to the protocol overhead required to manage multiple devices. Consequently, you're better off with one high-speed device compared to several slower peripherals if you're trying to tax interface bandwidth. Naturally, when we add devices to a USB 2.0 hub or FireWire daisy chain, the aggregate performance of those devices drops as well.

Despite impressive sequential results, Thunderbolt's random I/O performance is substantially weaker—often the case when you're working with external interfaces. Dropping an internal SATA drive into an enclosure with some sort of bridge chip negatively affects the disk's native potential. This can be attributable to the interface itself. For example, USB and FireWire completely discard command queuing, resulting in benchmarks the would seem to reflect a queue depth of one at all times. The graph below illustrates:

It is no surprise to see the hard drives deliver low throughput in a test involving random reads. But we'd expect to see SSDs doing better. Of course, our expectation there is based on the performance of a drive attached via native SATA (a 240 GB Vertex 3 should hit ~325 MB/s) at high queue depths. With one outstanding command, the Vertex 3 falls closer to ~70 MB/s. But the USB- and FireWire-based solutions even come up short of that number. What's going on?

Let's examine the random I/O performance of our external RAID enclosures. If these connectivity technologies cannot queue up commands, can we compensate through the use of multiple drives? After all, these RAID devices have their own own controllers to manage I/O requests, hence the support for hardware-based RAID.

Random I/O still looks pretty bad, even with multiple SSDs in RAID. It's simply bad here. Even with SSDs in RAID, we cannot achieve the same performance possible with a native SATA connection. Even the Pegasus R6 equipped with six Crucial m4 SSDs cannot seem to get past 80 MB/s. Although we're seeing generally-poor handling of random I/O by external interfaces, there are two exceptions where this wouldn't be the case.

First, a non-RAID eSATA drive should be able to achieve native SATA 3Gb/s performance, as long as it does not support any other interface. It must be non-RAID and exclusively eSATA because adding support for RAID and other interface technologies requires controller hardware. Lacie’s 4big Quadra, for example, cannot achieve native SATA performance via eSATA because it uses Oxford Semiconductor's OXUFS936QSE, a universal interface-to-quad-SATA storage controller (supporting eSATA, FireWire 800, FireWire 400, and USB 2.0). The RAID controller within the Oxford Semiconductor chip is implemented after the eSATA switch, affecting random I/O performance. Unfortunately, only a handful of external enclosures support eSATA and only eSATA.

Non-RAID Thunderbolt devices are also an exception. Inside them, you'll likely find a PCIe-to-SATA controller. This is very similar to the topology motherboard vendors used to add SATA 6Gb/s support to their platforms before it was integrated into chipsets, employing third-party Marvell and ASMedia controllers attached to the core logic through one PCIe link.

Non-RAID Thunderbolt drives employing third-party SATA controllers underperform native SATA connections, though, in this case. Seagate's GoFlex Thunderbolt adapter, for example, uses ASMedia's ASM1061 SATA controller, which coincidentally is also on-board our MSI Z77A-GD80. Theoretically, random performance should be nearly identical from both devices. But the GoFlex Thunderbolt adapter only delivers 120 MB/s, whereas we can achieve 160 MB/s with a direct connection to motherboard's ASM1061.

According to ASMedia, the performance of its ASM1061 depends on vendor-specific BIOS optimization. Creating a product for a broader range of applications, like the GoFlex, means less of the tuning you'd find on a piece of hardware tweaked for a certain motherboard model.

Sequential performance isn't as sensitive to those optimizations, which is something we also see in our SSD reviews. While we keep our BIOS, drivers, and SSD firmware up-to-date, sequential numbers rarely change. Not surprisingly, then, we see identical performance from our Vertex 3 in Seagate's GoFlex Thunderbolt adapter and MSI's Z77A-GD80. Both deliver a maximum of 400 MB/s in sequential reads.

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Top Comments
  • 22 Hide
    shoelessinsight , June 12, 2012 4:52 AM
    Active cables are more likely to have defects or break down over time. This, plus their high expense, is not going to go over well with most people.
  • 21 Hide
    mayankleoboy1 , June 12, 2012 4:35 AM
    thunderbolt will fail after external PCIE standard is implemented
  • 19 Hide
    Pyree , June 12, 2012 4:23 AM
    I was really hoping to see some eGPU benchmark. Oh well, I guess I have to wait.
Other Comments
  • 19 Hide
    Pyree , June 12, 2012 4:23 AM
    I was really hoping to see some eGPU benchmark. Oh well, I guess I have to wait.
  • 21 Hide
    mayankleoboy1 , June 12, 2012 4:35 AM
    thunderbolt will fail after external PCIE standard is implemented
  • 15 Hide
    mayankleoboy1 , June 12, 2012 4:36 AM
    for more insight of thunderbolt fail and Intel's lying :

    http://semiaccurate.com/2012/06/06/intel-talks-about-thunderbolt/
  • 22 Hide
    shoelessinsight , June 12, 2012 4:52 AM
    Active cables are more likely to have defects or break down over time. This, plus their high expense, is not going to go over well with most people.
  • 5 Hide
    A Bad Day , June 12, 2012 5:39 AM
    Looks like I'm going to steer clear of Copperpeak for my future build.
  • 16 Hide
    GI_JONES , June 12, 2012 5:43 AM
    Cost is going to kill this.
  • 12 Hide
    mayankleoboy1 , June 12, 2012 6:25 AM
    ^
    because "thunderbolt" sounds much sexier than "HDBaseT " ?

    and with apple, its all about the sexiness, not functionality/practicality.
  • -1 Hide
    JOSHSKORN , June 12, 2012 6:35 AM
    Prediction: We will see Thunderbolt available on SmartPhones. When we do, this port will be able to handle a monitor, external hard drives, speakers and many other USB devices through its Thunderbolt docking station. Obviously a SmartPhone won't need to be attached to a webcam. This will become the future desktop...that is, if it can run Crysis. LOL Had to add that in there. :) 
  • 3 Hide
    pepsimtl , June 12, 2012 7:02 AM
    I remenber scsi interface ,so expensive ,just the company (server) use it .
    and sata interface replace it.
    For me Thunderbolt is the same song
    I predict a sata 4 (12gb) or usb 4 ,soon
  • 13 Hide
    archange , June 12, 2012 7:21 AM
    Hot, expensive active cables cannot be anything else than niche.
  • 7 Hide
    emad_ramlawi , June 12, 2012 7:31 AM
    Technology for the rich ...

    i can wait a couple of minutes for files to be copied on USB 3.0 which is universal and open standard .

    thanks intel but ill pass
  • 4 Hide
    rex86 , June 12, 2012 7:43 AM
    I really hope that this is going to be another flop. USB3 is just fine for almost everything. I do agree that we need open external PCIe standard. We're already paying too much to Intel.
  • 6 Hide
    beetlejuicegr , June 12, 2012 9:46 AM
    Only thing usefull i can see right now is a laptop with intel/amd gpu using it to get access to high end external discrete gpu. All the other possibilities are not needed to be through thunderbolt.
  • -1 Hide
    Anonymous , June 12, 2012 10:15 AM
    What is 125oF in real measurements?
  • 0 Hide
    chesteracorgi , June 12, 2012 12:29 PM
    Thunderbolt is a wonderful innovation and alternative, but hardly ready for prime-time. Even on the Mac platform there is a derth of devices that use thunderbolt. Will thunderbolt be USB or Firewire?
  • -2 Hide
    A Bad Day , June 12, 2012 1:22 PM
    emad_ramlawiTechnology for the rich ...i can wait a couple of minutes for files to be copied on USB 3.0 which is universal and open standard . thanks intel but ill pass


    And if USB 3.0 is too slow, then use two of them (flashdrives in RAID 0 anyone?).
  • 2 Hide
    Anonymous , June 12, 2012 1:38 PM
    I can't believe how narrow some other people comments are. This new standard is for high end users and later others as well once prices start to drop. USB3 eSata when you are working with files that are 10s of Gigs in size are just too slow. Thunderbolt is fast plus easy plug and play for so many future possibilities. There are already a number of hard drives, raids arrays, Displays and now expansion Link PCIe adapter from Mlogic. Already it's potential is becoming interesting.
  • 1 Hide
    josejones , June 12, 2012 2:04 PM
    What are the costs of these new Thunderbolt ports on new z77 motherboards and are they 3rd party?

    I was considering getting the new Gigabyte Z77X-UP5 TH for my new i7 build but, not because of the Thunderbolt ports, but rather, due to the alleged lower mobo temps, which I'm concerned about with our 85F (31C) indoor temps. I await a serious review. These new boards are supposed to be available by the end of June:

    Gigabyte's Hardcore Thunderbolt Demo with GA-Z77X-UP5 TH Motherboard
    http://www.youtube.com/watch?v=deImUH8aUHQ

    Gigabyte Ultra Durable 5 at Computex, shows much lower temperatures
    http://www.youtube.com/watch?v=rLggGetNR14

    z77 Motherboard Discussion
    http://www.tomshardware.com/forum/308058-30-motherboard-discussion
  • 1 Hide
    josejones , June 12, 2012 2:17 PM
    ^ "are they 3rd party?"

    of course not = Intel
  • 1 Hide
    rantoc , June 12, 2012 2:25 PM
    I don't see this tech taking off in the consumer sector any day soon, its to expensive compared to the alternatives and with active cables it ensures that it will remain so! Few have use of the extra bandwidth provided where an usb3 will remain more than sufficient for the masses and the equipment/cables remain cheap!
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