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

[Alan McKinnon]

On Thu 11 August 2011 11:27:13 Grant did opine thusly:
> >> 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?

B and b mean whatever the fuck the manufacturer felt like having them 
mean on any given day[1]. There's no rhyme or reason with disk 
manufacturers, so you have to resort to independant testers who will 
tell you that disk have usable capacity of X units, where units is an 
exactly defined thing that we all understand.

[1] There are standards, but not enforceable so manufacturers can 
often do anything they want. Japanese sound amplifiers are the same - 
I've seen portable Sony units advertised as 5,000W!!!!!

That's two hot water geysers, a stove and a few kettles of power. All 
out of size D torch batteries. yeah right.

-- 
alan dot mckinnon at gmail dot com