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In article <C1FwFo.G63@jti.com> richb@jti.com (Richard Braun) writes:

>Using a simplistic disk performance test program provided by a drive
>manufacturer, I came up with the following surprising result:
>
>	The 8-bit Seagate ST02 is nearly 3 times faster than the
>	16-bit bus-mastering Adaptec 1542A.
>
>Why might this be?

Let me guess - the test program was published by Seagate?

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In article <C1FwFo.G63@jti.com> richb@jti.com (Richard Braun) writes:
>Using a simplistic disk performance test program provided by a drive
>manufacturer, I came up with the following surprising result:
>
>	The 8-bit Seagate ST02 is nearly 3 times faster than the
>	16-bit bus-mastering Adaptec 1542A.
>
>The program measures transfer rate, average seek time, track-to-track
>seek time, and a so-called "performance index".  With the drive
>low-level formatted for the Seagate's disk geometry, I get 3.5ms
>track-to-track time and a 30 performance index.  Reformatted for the
>Adaptec, the numbers are 4.9ms and 11.6.
>
>Why might this be?  Is it the different head/sector mapping (64 vs. 63
>heads, I think), or is the Adaptec just plain slower?  Is it possible/helpful
>to optimize the controller/device driver to match the physical disk
>characteristics (15 heads, 1632 cylinders)?
>

Seek tests done via BIOS for IDE and SCSI disks are completely 
bogus.  A track->track seek may not go off of the current track if 
the logical # of sectors per track > the real #.  

SCSI supports a seek command, but a disk doesn't have to do ANYTHING when 
it sees it.  The BIOS on the controller doesn't have to do ANYTHING.

As far as transfer rate, not using the hardware handshaking on the 
Seagate (enabled with the 0ws jumper), being "safe" and checking 
the SCSI status bits, you won't be able to transfer at > ~600K/sec.

I know the adaptec has no problems above those speeds.

Benchmarks need to be taken with a grain of salt, and need to 
be relevant.  

Finally, the Adaptec has more intelligence than the seagate, so you 
won't waste serious amounts of time in the kernel manually twiddling 
the SCSI bus.  This will leave more time available for user processes,
and your interactive performance on a real OS will be VASTLY superior
to what the Seagate can give you.

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