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Discussion on:
USB 3.0 arriving - bring on the speed

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The key question's going to still be overhead
-hh 15th Jan 2009
Its understandable that there's going to be some degree of conflict and competition for USB3 -vs- eSATA -vs- FW3200.

Similarly, it is straightforward for any of who are technologists to recognize that they're simultaneously both similar and different: their sponsors have slightly divergent goals, which results in different design priorities and trade-offs.

Insofar as eSATA, we should also remember that eSATA began as an internal SATA cable that was externalized to the host and was a klunge with headaches. While these have finally been sorted out, they didn't necessarily capture key marketplace customers such as Firewire has done (Video; transporation).

In terms of I/O performance, for a single-spindle hard drive, it is the HD that's the bottleneck, so there was no real practical differences between FW800, SATA-I, eSATA and now USB3 as well. However, RAID arrays can go higher, so some of the differences can now show up there...but that footnote is relevant to only the proverbial ~5% of the ~5% portion of the market (ie, the few that actually run external RAIDs).

In any event, USB3 has all of the indications of repeating the same issues that USB2 has had: the specification talks to its peak theoretical bandwidth, but disclosure by its sponsors as to what percentage of bandwidth is lost to overhead invariably seems to never be mentioned. I've found some documentation for USB2 that says that it has a ~40% bandwidth loss due to protocol overhead. Similarly, FW3200 has stated that its I/O will be 97% of its bandwidth, indicating only a 3% overhead loss.

So while we as technologists can all run through the numbers to see what overhead % rate that USB3 has to improve by in order to match the FW3200 performance, the non-technical reality is that the sponsors of USB3 are going to force its broad adoption and its going to be another example of "Better" being killed off by "Good Enough".

While I do appreciate the likely-large gains that USB3 will provide over USB2 (and even FW400 and FW800), what I actually do *not* look forward to is USB3 in the plug-compatible design interface that they've promised. It is going to make it very painful for the lay-person to actually wire up his system to actually get USB3-level speeds, because while the plugs are technically backwards compatible, this is effectively a disservice, since a USB3 device plugged in with a USB2 cable (or hub) will only be able to achieve USB2 speeds, since there's a piece of fiber missing along the path between PC and peripheral.

And finally, since the USB2-"B" plug is an utterly horrible design from a human interface perspective, even if USB3 is a success in the marketplace, I will nevertheless loathe it for perpetuating the loatheful design instead of killing it for anything better. If nothing else, the Firewire plug interface design is less bad.

-hh
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