USB 3 vs Thunderbolt

Posted on December 8, 2012 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.

Larry

23 Responses to USB 3 vs Thunderbolt

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Larry says:

December 11, 2012 at 9:48 pm

Bill:

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.

Larry
nsaati says:

December 11, 2012 at 11:07 pm

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:

December 11, 2012 at 11:22 pm

Nsaati:

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.

Larry
JL says:

December 13, 2012 at 5:40 am

Larry.

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

Thanks!
rick broat says:

December 17, 2012 at 6:10 pm

Nsaati:
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.
Charles Tomaras says:

December 17, 2012 at 9:41 pm

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.

See:
http://en.wikipedia.org/wiki/List_of_device_bit_rates#Peripheral
Larry says:

December 17, 2012 at 11:46 pm

Charles:

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.

Larry
Jeff Kirkland says:

December 20, 2012 at 5:02 pm

An excellent and well timed article. I unpacked my 27″ iMac on Monday and have been trying to make sense of my storage options ever since.

The one thing I’ve found out about USB3 drives this week is that they can vary in speed, even across the same make and model. I had three Seagate GoFlex desktop drives from another project, all purchased at the same time. They range in speed from 80MB/s to 140MB/s across the three using the same interface and cable.

I’m coming to the conclusion that the best way forward is to buy an enclosure and add my own drives so that I know exactly what’s in the box.
Jason Lavish says:

December 30, 2012 at 3:28 pm

So let’s get this straight… If I have just a single drive enclosure on either USB 3.0 or Thunderbolt, my actual transfer speed will only top out at 100MB/sec? And if that is so, then what am I getting right now with my single 3G HDD enclosures running on eSATA or Firewire 800?
Larry says:

December 30, 2012 at 3:32 pm

Jason:

Using today’s technology, the speed with which a single drive can transfer data ranges between 100 MB/second and 150 MB/second. If you are using protocols like FireWire. USB2, or iSCSI your transfer speed will be slower than that because the protocol can’t keep up with the drive. If you are using USB 3, eSATA, or Thunderbolt the protocol is fast enough to keep up with the drive.

For example, FireWire 800 tops out around 85 MB/second, regardless of how fast your drive is going, due to limits in the FireWire protocol.

Larry