02-21-2007, 04:37 PM

This is an oft discussed topic, but I figured I would add some personal experience to the mix here. To start with, we all know that USB-2 has a theoretical throughput of 480Mbits and Firewire has a theoretical throughput of 400Mbits. Based on that one would assume that USB-2 would be as faster than FW, right? The reality is MUCH different.

I am in the process of ripping my entire DVD collection to iPod viewable format with MediaFork (big surprise huh?). I have (well HAD) 3 DVD drives hooked up to my Mac, 1 internal and 2 external Firewire. I had wanted to buy a fourth drive and picked a new Lacie FW drive. In short, the Lacie did not play well with the existing devices on my FW bus and I ended up retuning it to Apple. After a bit of searching I found an external Lacie USB-2 slim line drive at MacMall for about $90.

The drive arrived yesterday and I eagerly opened it and set it up. I plugged the drive in, inserted a disc, the disc mounted, I queued up some episodes and hit rip. The rip topped out at about 12-13 Frames Per Second (FPS). That seemed slow, so I stopped the rip, queue the same DVD up in a FW drive and BAM!, 55FPS out of the gate. I tried a different DVD in the USB-2 drive, same thing 12-13FPS max sustained rate. USB-2 could just not handle the throughput I was used to despite the fact that it's architecture is designed to do so. The FW bus only has 4 devices on it, the USB bus has many.

The lesson here is that despite the theoretical advantages and architecture of USB-2, FW 400 is significantly faster in the real world. I found this on the USB-2 Wiki page:

The signaling rate of USB 2.0 Hi-Speed mode is 480 Mb/s, while the signaling rate of FireWire 400 (IEEE 1394a) is 393.216 Mb/s. USB requires more host processing power than FireWire due to the need for the host to provide the arbitration and scheduling of transactions. USB transfer rates are theoretically higher than FireWire due to the need for FireWire devices to arbitrate for bus access. A single FireWire device may achieve a transfer rate for FireWire 400 as high as 41 MB/s, while for USB 2.0 the rate can theoretically be 55 MB/s (for a single device). In a multi-device environment FireWire rapidly loses ground to USB: FireWire's mixed speed networks and long connection chains dramatically affect its performance.

The peer-to-peer nature of FireWire requires devices to arbitrate, which means a FireWire bus must wait until a given signal has propagated to all devices on the bus. The more devices on the bus, the lower is its peak performance. Conversely, for USB the maximum timing model is fixed and is limited only by the host-device branch (not the entire network). Furthermore, the host-centric nature of USB allows the host to allocate more bandwidth to high priority devices instead of forcing them to compete for bandwidth as in FireWire.

Despite all this and despite USB's theoretically higher speed, in real life benchmarks the actual speed of FireWire hard drives nearly always beats USB 2.0 hard drives by a significant margin.[10] In addition to this, some operating systems take a conservative approach to scheduling transactions and limit the number of transfers per frame, reducing the maximum transfers from, say, the theoretical 13 per frame to 10 or 9.

Now, anyone want to buy a nice USB 2 DVDROM/CDRW drive for their laptop?

02-21-2007, 04:40 PM

Great post.

I did my own homebrew test with a 25GB folder on my Mac Mini.

It took around 10 minutes with FireWire, around 25 minutes with USB.

02-21-2007, 04:49 PM

I noticed it when I got my iPod Video. it took considerable longer to do a full sync with that, then it did with my 4th gen iPod.

02-21-2007, 05:18 PM

Very nicely done baggss!

02-21-2007, 06:18 PM

I use PathFinder to do all my heavy duty file management. One of the things its file copy dialog gives you is a real time updating transfer rate. I have noted that using my G-Force FW-400 250 GB external hard drive, I can get up to 31 MB/s, which is certainly not at the FW maximum, but is pretty good.

So far, the fastest I have observed with a USB-2.0 drive is in the area of 12 MB/s.

Of course this may not be a fair comparison since the G-Force drive is the newest drive and hence presumably has the most advanced electronics. Still, it is an interesting data point and concurs with what baggss is pointing out above.

02-21-2007, 06:23 PM

Excellent post Baggss. I also have done a similar test and got the same results.

02-21-2007, 07:34 PM

Originally Posted by StretchR

I noticed it when I got my iPod Video. it took considerable longer to do a full sync with that, then it did with my 4th gen iPod.

Ditto here! I had a 3G iPod and uploads were so much faster than this 30GB Video iPod with the stoopid USB connector.

The other night I had about 35 tunes to upload on the iPod and it took around an hour for the sync. The tunes were in .aiff format but still...

And with the FireWire connector, I could let the iPod charge even if the Mac was shut down. With the USB connector, I have to have the iMac running or it's a no-go. :radioacti