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From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.sgi,comp.periphs.scsi
Subject: Re: < Connecting Fujitsu M2266SA to SGI SCSI (SOLVED) >
Message-ID: <21924@cbmvax.commodore.com>
Date: 25 May 91 05:45:15 GMT
References: <41530@unlisys.in-berlin.de> <41691@unlisys.in-berlin.de> <1991May13.160731.6804@neon.Stanford.EDU> <1991May14.151513.1347@utstat.uucp>
Reply-To: jesup@cbmvax.commodore.com (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 34

In article <1991May14.151513.1347@utstat.uucp> tg@utstat.uucp (Tom Glinos) writes:
>	Synchronous SCSI is never enabled on IO2 or IP4 machines, because
>	there would be no performance benefit.  SCSI transfer rate is
>	limited by how fast data can be pushed from the 3393 into memory,
>	and not by how fast it can be pulled off the SCSI bus.  Therefore,
>	it was decided not to enable this feature, since the only thing
>	it could do would be to cause problems."

>Still not satisfied I'm trying to get the very last drop of performance
>out of the drive. Why won't it run any faster than 900KB? The drive is
>rate for 2MB/sec in asynch mode. 
>
>A call to Fujitsu indicated that 
>	"in my configuration 1MB/sec was a good number." 
>
>The nuance of the phone call was that unless you had some VERY good
>SCSI equipement your aren't going to get anything near 2MB/sec.

	Well, the 33c93a can run an ST1480N and a Q210S at full bore at the
same time (both running disk performance tests (DiskSpeed 3.1)).  The 1480
gets between 1.5 and 2.0MB/s and the quantum gets 700-900K/s (at the same
time!)  That's on an Amiga A3000, 25Mhz '030, WD33c93a SCSI chip, with
Commodore custom DMA/FIFO chip(s) transferring the data to memory with longword
DMA cycles.  BTW, those speeds above are through the filesystem, which
generates direct DMA reads for large aligned transfers when possible.

	Their interface to the 33c93 might be inefficient (PIO a byte at a
time, perhaps).  Perhaps the 33c93 is far slower than the 33c93a.

-- 
Randell Jesup, Jack-of-quite-a-few-trades, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.cbm.commodore.com  BIX: rjesup  
Disclaimer: Nothing I say is anything other than my personal opinion.
"No matter where you go, there you are."  - Buckaroo Banzai