Re: [gentoo-user] {OT} USB 3.0 hard drive speed test

[Mark Knecht <markknecht@gmail.com>]

On Thu, Aug 11, 2011 at 11:27 AM, Grant <emailgrant@gmail.com> wrote:
>>> I'm testing this USB 3.0 bus-powered hard drive:
>>>
>>> http://www.amazon.com/gp/product/B0041OSQ9S
>>>
>>> and I get:
>>>
>>> # hdparm -tT /dev/sdb
>>> /dev/sdb:
>>> Timing cached reads:   8006 MB in  2.00 seconds = 4004.33 MB/sec
>>> Timing buffered disk reads: 252 MB in  3.01 seconds =  83.63 MB/sec
>>>
>>> # hdparm -tT /dev/sdb
>>> /dev/sdb:
>>> Timing cached reads:   8230 MB in  2.00 seconds = 4116.54 MB/sec
>>> Timing buffered disk reads: 252 MB in  3.02 seconds =  83.55 MB/sec
>>>
>>> # hdparm -tT /dev/sdb
>>> /dev/sdb:
>>> Timing cached reads:   8446 MB in  2.00 seconds = 4224.36 MB/sec
>>> Timing buffered disk reads: 230 MB in  3.02 seconds =  76.28 MB/sec
>>>
>>> Wikipedia says USB 3.0 has transmission speeds of up to 5 Gbit/s.
>>> Doesn't MB/sec denote mega*bytes* per second?
>>>
>>> - Grant
>>
>> 4000MB/s = 4Gb/s
>
> OK, I thought "B" designated bytes and "b" designated bits.  So when
> you see something like MB/s or Mb/s there's no way to know if it's
> referring to megabits or megabytes?
>
> - Grant

Nahh, I made a mistake there. 4000MB/S = 4GB/S  - You are correct, at
least as far as I'm concerned.

Of course Volker, the man with the answer to everything, just told you
that 80 mega-bit / second was a 'really, really good hard drive' so I
guess we all make mistakes. ;-)

I was really trying to point out that you ARE getting 80% of the USB
3.0 spec in the first number which is the speed of communications
across the USB cable talking to the drive interface. Sustained storage
rates of the drive don't have anything to do with that though. That
depends on the drive in the case.

Cheers,
Mark