SCSI and 386/ix

[John L. Grzesiak]

In article <25c1fdd8:490comp.unix.i386 at nstar.UUCP>, akcs.larry at nstar.UUCP (Larry Snyder) writes:
> I am considering using a Miniscribe 9380S as my primary drive
> here at nstar - and would like to know if the difference in
> throughput between the above drive running SCSI and a 18ms
> RLLed drive running on a 2372B will be that noticeable.
> 
> I assume that 386/ix will support a SCSI host adapter with
> a floppy drive adapter as a drop in replacement for the
> 2372B (so I won't need a seperate controller for the floppy
> drives).
> 
> Comments?  Ideas?  Has anyone else gone this route?
> 
> larry

I do a bit of interactive R&D at work, here are a few numbers:

8 Mb transfer to null with : dd if=/dev/dsk/0s1 of=/dev/null bs=8k count=1024.

RLL -wd1003            ESDI -wd1007vse2          SCSI -adaptec 1542A
CDC-85 mb              CDC-182 10mbps            CDC-385H
3:1 interleave         1:1 interleave            1:1 interleave
no track buffering     track buffer cached       Read Ahead Enabled

  raw 1:32.4           raw 12.2                  raw 13.8
block   57.3         block 14.0                block 13.5

Notes:
	The track buffering on the WD1006vsr2 will be closer to the ESDI
 performance but will not boot or run ISC 2.0.1. or 2.0.2. The Adaptec
 ESDI (2322) was not much faster than the WD1003!! (About 32 seconds in block).
 Chantal was tested on the SCSI (ver 3.02 and 3.51) . It showed a minor 
 decrease in raw and block transfer but an overall increase in loaded system
 performance. The SCSI figures are also slightly deceptive since the amount
 of system time required to do the transfer was less than half the WD 
 interface controllers. The EDSI and RLL performance also decreases by a
 factor of two with dual drives. SCSI showed no such problem with two (or
 more) drives. 

Comments and conclusions.
	ESDI and RLL are still Programmed I/O type controllers requireing
 	nearly full CPU attention, as well as being limited by the speed
	of the transfer rate. (i.e. a 10mbs ESDI setup with two drives
	will allow each drive to transfer about 5mbps). ESDI is limited
	to two controller on ISC (4 drives). With 4 Maxtor 768mb 15 mbps
	drives , maximum capacity is 2.4 gbytes formatted.

	SCSI is an 8megabyte transfer rate, DMA controller capable of
	transferring without processor intervention. Direct ISC support
	is two controllers and 4 drives (2.4 gbytes) or with 3rd party
	Chantal .. 3 controllers and many drives. Plus DAT tape support.

	My vote is SCSI..... 
	just make sure you use Adaptecs controller and Enable read
	ahead on your drives. You will be super satified.

	*-----------------------------------------------------------------*
	* John Grzesiak @ Omega Dynamics :  Specializing in UNIX/XENIX    *
	* Meriden Ct USA                 :    Consulting . . .            *
        * jlg at odicon or spock!odicon!jlg : gaboon!odicon!jlg              *
	*-----------------------------------------------------------------*