Date: Tue, 2 Apr 1996 21:33:34 +0800 (WST) From: Terry Dwyer <tdwyer@netbsd08.dn.itg.telecom.com.au> To: Michael Smith <msmith@atrad.adelaide.edu.au> Cc: Zeki Basbuyuk <Zeki@Dilbert.Oasysinc.com>, stable@FreeBSD.org Subject: Re: SCSI Performance under -stable/-current Message-ID: <Pine.BSI.3.90.960402212118.585C-100000@netbsd08.dn.itg.telecom.com.au> In-Reply-To: <199604021022.TAA14221@genesis.atrad.adelaide.edu.au>
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On Tue, 2 Apr 1996, Michael Smith wrote:
> Zeki Basbuyuk stands accused of saying:
>
> > How do you get this speed? I thought there is a physical limitation
> > on how much speed you can get for a hard drive. The calculation is
> > as follows. 120 rps (revs per sec assuming 7200 rpm drive) X 40
> > sectors per track (average or above average) X 512 bps (bytes per
> > sector) = 2.4 MB /sec. To get 6 MB either spt needs to increase to
> > 100 or so or rotation needs to be increased.
>
> One should always temper theory with reality. You can go a lot faster by
> striping your sectors across several surfaces, for example.
For example, multiply the above figure by the number of physical heads on
the drive, 5 for a barracuda. It looks like he's only calculated for one
head. I also seem to remember reading somewhere that the _internal_ data
transfer rate was about 47 to 70Mb/sec., at least for a barracuda.
>
> Reality shows us that the more agressive drives will happily outrun the
> sustained rate your envelope calculation suggests, so I guess reality is
> more complicated that you're allowing for 8)
>
> > Tom
>
> --
> ]] Mike Smith, Software Engineer msmith@atrad.adelaide.edu.au [[
> ]] Genesis Software genesis@atrad.adelaide.edu.au [[
> ]] High-speed data acquisition and (GSM mobile) 0411-222-496 [[
> ]] realtime instrument control (ph/fax) +61-8-267-3039 [[
> ]] Collector of old Unix hardware. "Where are your PEZ?" The Tick [[
>
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