Newsgroups: comp.periphs
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: SCSI->SCSI vs. SCSI->ESDI disk performance?
Message-ID: <1989Jul19.170414.20326@utzoo.uucp>
Organization: U of Toronto Zoology
References: <398@sunny.ucdavis.edu>
Date: Wed, 19 Jul 89 17:04:14 GMT

In article <398@sunny.ucdavis.edu> poage@sunny.ucdavis.edu (Tom Poage) writes:
>Is there a performance hit in having an ESDI disk
>hooked to a SCSI bus through a translator (Emulex MD21)
>versus a SCSI disk hanging directly on the bus?

The odds are very good that your "SCSI disk" is in fact an ESDI disk or
something similar with such a translator built in.  No disk drive directly
talks SCSI; there has to be a controller in there somewhere, even if it's
built into the drive.  Many manufacturers supply the same drive as a SCSI
drive or an ESDI (or whatever) drive simply by leaving out the controller
board and the SCSI connector if the order doesn't say "SCSI".

Any difference in performance will be a matter of controller design, disk
data rate, etc., and close attention to the specs is needed.

>ESDI disk performance is supposed to be higher than
>that of SCSI disks...

*If* the ESDI drive is hooked directly to your machine, not via SCSI.
Running it through a SCSI translator eliminates any inherent performance
gain.

(Actually there is no inherent reason why SCSI drives can't be blazing
fast, it's just that most of them aren't.)
-- 
$10 million equals 18 PM       |     Henry Spencer at U of Toronto Zoology
(Pentagon-Minutes). -Tom Neff  | uunet!attcan!utzoo!henry henry@zoo.toronto.edu