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

[Grant <emailgrant@gmail.com>]

>>>> 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

As Volker pointed out, I don't think hdparm -T interacts with the USB
system at all.  I get the same rates whether the USB hard drive is
plugged into a 3.0 port or 2.0 port.

- Grant


> rates of the drive don't have anything to do with that though. That
> depends on the drive in the case.
>
> Cheers,
> Mark