[kwlug-disc] USB3 expectations? (was: Re: USB3 on Linux)

Khalid Baheyeldin kb at 2bits.com
Fri Jun 18 16:40:06 EDT 2010

On Fri, Jun 18, 2010 at 2:31 PM, unsolicited <unsolicited at swiz.ca> wrote:

> Khalid Baheyeldin wrote, On 06/18/2010 11:54 AM:
>> Something I would be interested in is transfer speed from a hard drive. Is
>> it really that different on USB3 from USB2, or will it be the same?
> Help me understand the question.
> If USB3 is faster than USB2, why would it be the same? Hw/sw not catching
> up to the specs yet?
> Or are you expecting the performance increase not worth the price?

I am not thinking OpenWRT at all here. Just backing up to a USB or eSATA
drive dock.

If you look here, the desktop fastest disk from about a year ago can do 104

So let us assume that an average disk is around 70 MB/s.

USB 2.0 is 60 MB/s nominally (same Wikipedia article you reference, table
further below), and the several year old server that I have can't even reach
that when backing up. The backup size is 90GB, and that should be around
25.6 minutes. However, the real time is around 1 hour 20 minutes.

So, if USB 3.0 is 300 MB/s (same Wikipedia article and table), and the disk
is still at 70 or 100 MB/s, then what is the benefit from going from USB 2.0
to USB 3.0?

For other applications, it may be useful. But when moving platters are
involved, there is no advantage yet.

I should caution that generalizing from the above may be a mistake, because
the bottleneck maybe somewhere else. Some observations: the backup spikes
the CPU considerably, despite this being a dual core machine. There is lots
of free RAM. It could be wait for I/O that is the bottleneck. Could be the
USB drivers are inefficient. Could be the dump utility's buffering is not
good (despite specifying a large block size). I am not sure.

Until this thread, I don't think I even knew there was such as thing as USB
> 3. So I poked wikipedia for some info. Thieving from wikipedia -
> http://en.wikipedia.org/wiki/Usb3#USB_3.0:

There are already USB 3.0 drive docks at the local Canada Computers stores.

P.S. My laptop from about a year ago came with a dual USB/eSATA port, which
I have not tried so far.
Khalid M. Baheyeldin
2bits.com, Inc.
Drupal optimization, development, customization and consulting.
Simplicity is prerequisite for reliability. --  Edsger W.Dijkstra
Simplicity is the ultimate sophistication. --   Leonardo da Vinci
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