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From: jdow@gryphon.CTS.COM (J. Dow)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech
Subject: Re: Hard Disk Performance tests, comments invited
Summary: Drive format matters a LOT
Message-ID: <8086@gryphon.CTS.COM>
Date: 23 Oct 88 22:53:45 GMT
References: <10150@cup.portal.com> <12391@steinmetz.ge.com>
Reply-To: jdow@gryphon.CTS.COM (J. Dow)
Distribution: na
Organization: Wizardess Designs, Hermosa Beach, Ca.
Lines: 77

In article <12391@steinmetz.ge.com> perley@rocky.steinmetz.ge.com (Donald P Perley) writes:
>In article <10150@cup.portal.com> thad@cup.portal.com (Thad Thad Floryan) writes:
>>Following are some most-interesting disk performance results.
>
>>   	The object of the comparisons are to show that "True DMA" controllers 
>>     are not always the best.  In fact, the fastest times were obtained using
>>     boards that use no DMA,  instead using polled I/O to read/write data.
>>     These were early tests and are not the fastest times obtained.
>>     These tests show the difference between the non DMA boards and DMA boards,
>
> > ............ a bunch of benchmarks ...............
>
>These show good data rates... GREAT!
>
>As comparisons between DMA and non-DMA, they show that:
>
>
>	non-DMA is faster than DMA
>
>	OR
>
>	Quantum pro-drives are faster than Seagate ST251-1 or Miniscribe
>	3053.
>
>	OR
>	
>	SCSI is faster than ST506
>
>	OR
>
>	The 2090 design is lacking in some other respect.
>
>
>
>
>Somehow, with all those variables involved, dma/non-dma doesn't jump
>out as the clear explanation. 
>
Well, now - one of the things that affects disk speed most dramatically is the
hard format interleave. If you take a drive optimized to run at best speed on
say the StarDrive and hook it to a HardFrame controller you'll hardly see any
speed change at all. But if you hard format the drive and experiment to find
the best interleave for your particular controller setup you will likely see
a very dramatic speedup of at least 2:1.

Another large factor is seek time. And with the way SCSI drives work it is
nearly impossible to separate seeks from pure data access within a track.

hence all comparisons must be done with the same SCSI drive (and code revision
of the SCSI controller code) in order to make any sense at all. Then the
benchmarker must reformat the drive, first to the controller card manufacturer's
suggested parameters for hard interleave and then to several others to find
the optimum. (StarDrive actually slows down with 1:1 interleave. HardFrame
seems to speed up all the way to 1:1 on my adaptec controller. (I am not about
to kill the ST277N for tests but indications are it is about the same to a
trifle faster.))

ANother thing to beware of in comparing drives is on board cache memory effects.
Usually when accessing a drive to load a program you are not pulling data from
the cache. So it will offer no perceptable speedup there. For a compile,
however, a cache can make a heck of a lot of difference.

This is why drive benchmarking and raw transfer rate figures are a tad hazardous
when taken alone. They do not often indicate what a user's perceptions of speed
might.
{@_@}

-- 
Sometimes a bird in the hand leaves a sticky deposit.
Perhaps it were best it remain there in the bush with the other one.

{@_@}
	jdow@bix (where else?)		Sometimes the dragon wins. Sometimes
	jdow@gryphon.CTS.COM		the knight. Does the fair maiden ever
	{backbone}!gryphon!jdow		win? Surely both the knight and dragon
					stink. Maybe the maiden should suicide?
					Better yet - she should get an Amiga and					quit playing with dragons and knights.