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Re: USB 3.0 for a 2.5" drive?

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On Sat, 08 Aug 2015 03:01:07 -0500, Robert Wessel
<robertwessel2@yahoo.com> wrote:

>On Sat, 8 Aug 2015 07:06:11 +0000 (UTC), "Charles T. Smith"
><cts.private.yahoo@gmail.com> wrote:
>
>>Hi, a quick question for the experts.
>>
>>I've gathered the impression that the interface technology (usb, sata, 
>>pata) for disk drives is really irrelevant - for a single drive - because 
>>disks can't deliver data fast enough to run into an interface bottleneck.
>>
>>Maybe that assumption's not correct... anyway, I see an ad for a Seagate 
>>external 2.5" drive which uses "USB 3.0 Super-speed, up to 10x faster 
>>than USB 2.0".  While that's likely true about USB 3.0, isn't it 
>>cynically, unethically misleading about the effect on the drive's 
>>performance?  Or, why would Seagate supply drives with USB 3.0 technology?
>>
>>I once did the numbers regarding cylinder, spin-rate, etc, but they say 
>>that these days those parameters are irrelevant ...
>
>
>They're not irrelevant.  Modern desktop spinning disk can hit transfer
>rates from the platter well over 100MB/s, at least for sequ3ential
>reads.  Enterprise drives are often in the 300MB/s range.  USB2.0 is
>limited to a theoretical 60MB/s, but as in practical terms rarely
>achieves more than about half that.  Also I/O to the cache onboard the
>drives can happen faster than that.  So USB 2.0 really is a bottle
>neck when performing bulk (sequential) I/O to a disk drive.  For
>random I/O, it makes little difference.
>
>Now as to whether or not USB 3.0 is *really* ten times faster is a
>different question (sure, the interface is ~10 times faster), but
>there's no doubt that things like backups to an external drive can run
>considerably faster with a USB 3.0 connection in many cases.  Backups
>are a major use case for external drives, so sequential performance
>*is* important.
>
>OTOH, the practical difference between SATA 1/2/3 and USB 3.0 is
>fairly minor.  OTTH, the difference between SATA 1 and SATA 3 is only
>a factor of four, and SATA 1 is 150MB/s anyway, far faster than USB
>2.0 (and SATA tends to use more of its theoretical bandwidth).
>Likewise the fastest PATA (133MB/s) interfaces have not been too far
>off keeping up with desktop drives until recently.
>
>In a sense the practical difference between PATA-133, SATA-1/2/3 and
>USB 3.0 are modest, but USB 2.0 (or say PATA-33) is actually
>substantially slower.


And here's an on-point Macworld article from a few years ago:

http://www.macworld.com/article/2039427/how-fast-is-usb-3-0-really-.html

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USB 3.0 for a 2.5" drive? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-08-08 07:06 +0000
  Re: USB 3.0 for a 2.5" drive? Robert Wessel <robertwessel2@yahoo.com> - 2015-08-08 03:01 -0500
    Re: USB 3.0 for a 2.5" drive? Robert Wessel <robertwessel2@yahoo.com> - 2015-08-08 03:05 -0500
  Re: USB 3.0 for a 2.5" drive? Richard Kettlewell <rjk@greenend.org.uk> - 2015-08-08 10:41 +0100
    Re: USB 3.0 for a 2.5" drive? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-08-09 20:19 +0000

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