Mylex SCSI Controller, 16550A UARTS

Karl Denninger karl at ddsw1.MCS.COM
Thu Oct 5 00:18:20 AEST 1989

In article <22709 at> cliffhanger at (Cliff C Heyer) writes:
>Karl Denninger Writes...
>>That's funny...
>>The WD1007/WA2 has been clocked here at 950KB/second (ESDI 10 Mhz).  I
>>understand that the WD1008 (15Mhz ESDI) has been clocked at over
>>1300KB/second, although I haven't seen that one myself.  The DPT boards 
>>have been clocked at that rate (950KB/sec) on cache misses.  On cache
>>hits the DPT board is off the top of scale on our tests; that is in 
>>excess of 4MB/sec!
>Michael Umansky Writes...
>>In my 25Mhz Micronics with 8Mhz AT bus and Adaptec AHA-1542A SCSI controller
>>and CDC WREN III SCSI drive I get about 900 KB/sec.  The Mylex controller
>>should deliver at least a magnitude more to be cost effective.
>Cliff Heyer Responds...
>I became interested in speed when I was asked to evaluate porting VAX applications
>to IBM PC/compatible micros. During my analysis & testing, I found the MIPS more
>than adequate in PC land, but disk I/O was the problem.
>The VAX ranges from 600KB/sec to 1.3MB/sec tops sustained I/O *per job*. Many
>PCs I tested got in the range of 200KB/sec (ST-506 ...). Then I found to my
>surprise that SCSI & ESDI disks on many machines was still 200-300KB/sec!  
>This was confirmed by checking BYTE benchmarks that list 1MB throughput times.
>SUN was the only machine in BYTE that showed a respectable 800KB/sec time.

Huh?  1.3MB/second per job, eh?

With what interface?  And to how many jobs?  We install, service, upgrade
and work on VAX systems all the time, and I've >never< seen one which can
sustain 1.3MB/sec (bytes now, not bits) across more than one or two jobs!

Now, there are exceptions I'm sure.  A big Vaxcluster with multiple spindles
and controllers, perhaps.  The typical 3xxx (or MVII) series machine with 
ESDI or SCSI interfaces and a couple of drives?  No way!

Wanna buy a 4 million dollar system?  Sure, I can provide what you want, to
many jobs.  It'll cost you about what most companies earn in a year!

>It has become evident to me that in spite of 15MHz ESDI chips, sync SCSI, etc.
>certain machines still go as slow as their ST-506 counterparts. Also, unlike
>the old mainframe days when computer were rated in actual disk I/O in KB/sec, 
>todays micros are sold with NO ratings, except the "chip throughput" ratings
>which are meaningless because they do not show what the actual throughput

I don't know where you're coming from, or where you get your hardware, but
there is no way that I can agree with this.

Sure, some OPERATING SYSTEMS can't keep up.  That's true of VMS too, you
know.  386/ix, in particular, is supposed to be a real screamer (we don't
use it here for completely different reasons related to support).  SCO isn't
quite as fast as the hardware; I'd admit that I have a darn hard time
getting better than 400KB/sec out of Xenix through the raw I/O interface.
That is something that needs to be taken up with the software vendor.

Every one of our RLL-based machines can do in the area of 700KB/sec raw I/O.
Every one of our ESDI-based machines can do in the area of 900KB/sec.  What
is lost in the OS is another story, but that's something we don't have
control over!

If we sell a 386 system with an RLL interface, you can bet we'll guarantee
that the raw I/O rate, measured with something like CORETEST (gotta define
the benchmark in order to be meaningful), is from 630-700KB/sec.  ESDI
drives are faster, we normally measure throughputs in the area of 900KB/sec.

Every machine IS checked for transfer rate before it leaves the building.

No, you can't do this with cheap and slow hardware.  You certainly CAN with
fast and a little more expensive components.

>So I have no way to know if the machine I want to buy has 900KB/sec I/O, 
>except from USENET. The sales people won't tell you anything. It seems that
>disk I/O is a big secret, all they want you to think about is MIPS. You are
>provided with NO information with which to make an informed configuration
>decision. As soon as you do some disk benchmarks you have to sign a non
>disclosure agreement. As a result, I have developed a somewhat cynical view that 
>these companies have a vested interest to saturate the market with slow I/O
>hardware, knowing that you will grow and later have to buy more hardware
>to get the 900KB/sec. Why sell you a better mousetrap if people are happy buying 
>the old one?

Why not buy from someone who does bother to check these things, and can tell
you exactly what you're getting?  Are you expecting to get this kind of
service (yes, it IS a service) from the "cheep" mail-order places?  You got
to be kidding!  

Buy from a place that knows what they're doing, a VAR (which is exactly
where you would have to go to get a SUN or DEC, unless you buy from the
manufacturer at full list!), and you will be able to get that information.

In writing if you require it.

Your vendor(s) won't do that?  Switch vendors.  We're out here (and I'm sure
we're not the only ones).

>I'm hoping that if I am wrong, someone will be able to give me a convincing
>argument otherwise.

You just got one.

>Cliffhanger at
>PS did any of you "shop" for 900KB/sec? If so, how did you establish this
>speed actually was possible before you bought?

Karl Denninger (karl at ddsw1.MCS.COM, <well-connected>!ddsw1!karl)
Public Access Data Line: [+1 312 566-8911], Voice: [+1 312 566-8910]
Macro Computer Solutions, Inc.		"Quality Solutions at a Fair Price"

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