From owner-freebsd-hackers  Mon May  8 13:41:04 1995
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Date: 	Mon, 8 May 1995 13:51:50 -0700 (PDT)
From: Tom Samplonius <tom@haven.uniserve.com>
To: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com>
cc: hackers@FreeBSD.org
Subject: Re: Is a 486 fast enough for SCSI?
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On Mon, 8 May 1995, Rodney W. Grimes wrote:

> It is not the CPU, but you failed to mention which version of 
> FreeBSD and particularly the ahc driver you are running.  I suspect
> that the driver may be detuned for compatibility reasons, but Justin
> is the one who would know best on that.

  I'm running a current kernel.  I've heard that tagged command queueing 
is disabled be default.  

> You also failed to mention the model of the drives, a parameters like
> RPM that greatly effect the raw data rate of the drive (if you have
> the media transfer rate number that is the best one to use, it is
> usually a range of values due to ZBR recording.  The higher number is
> what you get for the outer cyclinders, the lower number for the inner
> cylinders).

  Digital DSP3210S.  Media transfer rate is 2.5 - 5.5.  Drive performance 
doesn't really explain why performance is halved when two drives are in 
use.  Since PCI can handle up to a 130 MB/s, and FAST SCSI can do 10MB/s, 
two drives should be able to both run at 2MB/s simultaneously.

> I can easily do 4MB/sec using a DX33 EISA system with an AHB1742 controller
> and DEC 3053L disk drives (Media transfer rate is 2.5-5.5MB/sec).  This
> is with FreeBSD 1.x through to FreeBSD 2.x-current, but only because the
> ahb driver has been stable pretty much the whole time.

  I wish I had a EISA motherboard, as I have a slightly used 1742, and 
two 1740's laying around.


Tom