USB 3 vs Thunderbolt

Posted on by Larry

I’ve gotten a lot of questions recently on USB 3 vs. Thunderbolt, so I wanted to share what I’ve learned.  (By the way, I updated this to provide clarity on USB 3 speeds.)

Thunderbolt and USB 3 are both protocols for transferring data from one place to another. The easiest way to imagine that these are “pipes” that carry water. USB 3 is a big pipe. Thunderbolt is an even bigger pipe. The bigger the pipe, the more data it can transfer at one time.

Thunderbolt Is A Really Big Pipe

USB 3 has a top speed of 5 Gbps, which equals about 600 MB/second.  Thunderbolt has a top speed of 10 Gbps, which converts to 1.1 GB per second; which is about two times faster.

NOTE: Data speeds are often measured in bits per second (bps – note the lower case “b”). Hard disk speeds are generally measured in Bytes per second (Bps, note the UPPER case “B”).  To convert bps to Bps, divide bps by eight.  bps/8 – Bps.  I use Bps for all the speed measurements in this article.

Now, in order to hit those maximum speeds, you need to have a RAID containing at least five drives for USB 3 and ten drives for Thunderbolt. If your storage has fewer drives, it will still go fast, but it won’t “fill the pipe.”

NOTE: A quick way to estimate the speed of your device is to multiply the number of hard disks it contains by 100 MB/second.

USB 3 Can Have Problems

Fred offered a comment on my blog about “Configuring an iMac for Video Editing”:

I’ve been using USB 3 on the PC side for some time and the issues that Apple is having with it are not new and not Apple-exclusive. USB 3 is notoriously dicey. If you try to use a hub with it, it will become completely unreliable. Some early interface chipsets in the drives are very fussy with speeds ranging all over the map. I’ve had good luck lately with the newer stuff. The small Buffalo drive I got with both USB 3 and Thunderbolt seems to perform pretty well both ways on my Mac Mini. But my thinking is that Apple won’t have answers on the USB 3 issues for you because they aren’t specifically Apple’s issues.

Which to Pick?

Both Apple and Intel are aggressively reviewing all Thunderbolt devices – as part of their Thunderbolt Certification program – to make sure all new Thunderbolt devices meet the spec and play nicely with others. This is one of the reasons Thunderbolt storage is taking so long to come to market.

Architecturally, Thunderbolt is built for higher speeds than USB 3.0. My recommendation is use Thunderbolt for the best performance and reliability. If you need PC compatibility, use USB 3. Thunderbolt for Windows is coming soon and, when it arrives, is the best choice for maximum performance.

NOTE: As a side note, you can’t attach a Thunderbolt hard disk to a computer that doesn’t have Thunderbolt using a FireWire cable. I know because I tried, then learned from tech support that it doesn’t work that way.

As always, let me know what you think.


23 Responses to USB 3 vs Thunderbolt

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  1. Thomas Peterson says:

    I don’t get the last note. Why would you Thunderbolt and FW be compatible? Doesn’t make any sense to me…

    • Larry says:

      Ah, good point, I was a bit cryptic.

      When I bought my Thunderbolt drive, I discovered that the computer I was connecting it to did not have a Thunderbolt port. (There’s a message there about doing a bit of basic research before spending money that I’ve decided to overlook…)

      Anyway, there I was with the drive and the computer. I realized that Apple sells a Thunderbolt to FireWire converter cable. So, I bought it to see if I could connect the Thunderbolt drive to the computer via FireWire. The cables connect, but the way Thunderbolt is implemented, the drive vendor told me, you need to connect the Thunderbolt drive to the computer first, then connect the FireWire drives to the Thunderbolt drive using the FireWire converter cable.

      I have since tested this configuration and it works fine. Hence, my note.


  2. Norender says:

    Nowadays, maybe you should difference between SSD and HDD when you build a RAID. SSD write speed is double than HDD at least, then you need less drives. With two fast SSD you are taking profit of USB 3.0 bandwidth.

    • Larry says:


      This is a good point. However, USB 2, FireWire 400, FireWire 800, and iSCSI are too slow to take advantage of SSD drives, though SSD memory will speed up disk access, if not transfer.

      Some eSATA, mini-SAS, USB 3, and Thunderbolt drives will benefit from SSD, however, here you need to be aware of slowdowns introduced by system overhead. The new Drobo 5D and Drobo Mini, for example, do not benefit from using SSD drives in replacement of a standard spinning hard disk. Though they do benefit from adding a small SSD drive to boost file access.


  3. Stuart says:

    I’ve had an interesting conversation about thunderbolt today.

    A client told me they’d had issues with thunderbolt over long periods. They have been processing Red footage constantly and when it hits 6-7hour mark it falls over.

    Unfortunately I’ve not got a thunderbolt drive to test this. Shame if it’s true as a lot of productions I’ve got coming up have this kind of intense media processing.

    • Larry says:


      I don’t think that’s true. Back when Thunderbolt was first released, a lot of the early hardware was figuring out how the new protocol worked. Since then, both Apple and Intel have set up certification programs to be sure that all new hardware meets spec. I suspect what your friend was seeing was the perils inherent in being an early adopter.


  4. stu aull says:

    thanks as always for your time and insights!!

  5. Dylan Reeve says:

    Thunderbolt isn’t really like USB3 (or Firewire).

    Thunderbolt is basically a PCIexpress connection. If you’ve used an Avid DX I/O box, or a AJA IO Express you might be familiar with the PCIe expansion card and heavyduty cable they use. Thunderbolt is basically like that.

    Unlike USB where the computer has a USB controller and sends USB-formatted serial data back and forth, Thunderbolt is more like an externalised expansion card.

    A Thunderbolt drive, for example, basically has a SATA controller inside it, just as if it were a SATA expansion card for your computer.

    For this reason Thunderbolt can basically do anything that an expansion card can do (up to four PCIe lanes currently). But all the heavy lifting is done in the device at the end of the cable.

    However I believe the nature of Thunderbolt means it can’t support many devices in the way that USB3 can. Also I don’t think a Thunderbolt hub is possible.

    A mixture of both interfaces might be ideal for many users.

  6. Bill says:

    Quick comment on iscsi.. it is going to be network limited. If your network happens to be 10 gig ethernet (expensive) and that is connecting to a fast storage system (say with raid groups containing 16 x 15k rpm SAS drives, the iscsi won’t be a limitation. (You can also create arrays with SSD caching as part of that.

    Not cheaply, mind you. Noisy, expensive (very) and huge. but VERY fast and reliable. (Snapshot technology makes the act of taking a ‘backup’ snapshot less than a second on a lun there, then you spool the backup off to tape (again.. very expensive.)

    Oh – and you probably need a fiber switch for the ethernet as well. (10 gig ethernet requires watts of power for short copper runs, so dig deep if you want *fast*..

    • Larry says:


      All good comments, however iSCSI on a Gigabit Ethernet provides excellent speeds for general file transfers, backups, Time Machine and storing assets. And on a Gig Ethernet network, prices are very reasonable. In fact, downright cheap.


  7. nsaati says:

    anyone ever have any issues with a firewire drive using the firewire800 to TB adapter apple makes. i find it completely unreliable as the drive always ejects. It happens constantly at random, and i have turn hard disks off when possible checked off in the power options.. idk, im always frustrated by it… any ideas?

    • Larry says:


      Hmm… I only used this adapter a few times – to copy about 400 GB of data from three different FireWire drives to a Thunderbolt drive, but I don’t think I had any problems. The drives never became unmounted.


  8. JL says:


    Please keep us updated with more posts about how you end up setting up your own storage setup.


  9. rick broat says:

    I have been using the firewire800 to TB adapter apple makes to a voyager w. internal 2T drive and it has been fine, no problems, was hooked up for 10 hrs straight yesterday.

  10. Charles Tomaras says:

    The speeds quoted in your article are innacurate.

    USB 3.0 tops out at 5Gbit/s
    Thunderbolt is listed at 10Gbit/s x2

    I can’t quite figure where you got your numbers from for Thunderbolt and it appears you quoted the older USB 2.0 speed for USB 3.


    • Larry says:


      It is common, when measuring hard disk speeds to convert from bits per second (bps) to Bytes per second (Bps) simply because it makes the numbers more manageable. In this case, 5 Gbps = about 600 MB/second.

      I agree, the 480 MB/second I used in my article was a bit low and I’ll correct that.


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