Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!decwrl!public!thad
From: thad@public.BTR.COM (Thaddeus P. Floryan)
Newsgroups: comp.periphs.scsi
Subject: Re: speed difference on external drives?
Message-ID: <1893@public.BTR.COM>
Date: 24 Feb 91 00:48:52 GMT
References: <1991Feb23.194013.13400@unixland.uucp>
Organization: BTR Public Access UNIX, MtnView CA, Contact: cs@btr.com 415-966-1429
Lines: 24

In article <1991Feb23.194013.13400@unixland.uucp> bill@unixland.uucp (Bill Heiser) writes:
>
>Does having a SCSI drive external to a 386 system, on a cable
>several feet long, affect the data transfer rate?  Is it significantly
>better to have the drive mounted internally in the system?

No (re: data transfer rate).  Assuming a drive fits in your system's box, the
advantage of internal mounting is transportability of your entire system; a
possible disadvantage of internal mounting "may" be additional stress on your
system's power supply if the drive in question has large startup-current
requirements (such as the large Maxtor drives).

The system I'm sitting at right now (an Amiga) has a 20 foot single-ended
SCSI bus, properly configured, and sporting three large Maxtor drives, one
Quantum 80S, one Fujitsu tape drive and one Archive tape drive.  All SCSI
cabling is PROPERLY daisy-chained and terminated at both ends and is 100%
reliable; the last boot time was July 7, 1990 ... it's been up since then
(to be fair, the entire system is on a UPS).

Using the "DiskPerf" program, even the furthest drive (the Quantum) easily
achieves over 700Kbytes/S for reads and writes.  The additional several nS
delay at the end of the bus matters not one whit at SCSI speeds.

Thad Floryan [ thad@btr.com (OR) {decwrl, mips, fernwood}!btr!thad ]