Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!pyramid!octopus!pete
From: pete@octopus.UUCP (Pete Holzmann)
Newsgroups: comp.sys.ibm.pc
Subject: Re: FAST disks on PC AT clones
Message-ID: <212@octopus.UUCP>
Date: 3 May 88 08:38:33 GMT
References: <21346@amdcad.AMD.COM> <205@octopus.UUCP> <1006@spdcc.COM> <613@mccc.UUCP>
Reply-To: pete@octopus.UUCP (Pete Holzmann)
Organization: Octopus Enterprises, Cupertino CA
Lines: 91
Summary: Use 1:1 interleave controller. Use RLL if you can. ESDI even better!

In article <613@mccc.UUCP> pjh@mccc.UUCP (Pete Holsberg) writes:
>
>Has anyone found that the controller has a big effect on HD performance.
> I have a Micropolis 1335 (71MB formatted, 28ms) drive with a DTC 5280
>controller in a 386 box, and the Infoworld benchmark says that it is a
>dog!  CORETEST 2.4 and PC Mag Benchmark suite 4 agree that it is a 28 ms
>drive!  Steve Satchell (IW) has yet to answer this question about what
>the IW test does that might make this combo look so bad.  Perhaps one of
>you has a thought??  Thanks.

The controller has little to do with seek times. It should also be noted
that for many applications, average seek time has almost nothing to do
with performance, either!

For most applications, DATA TRANSFER RATE is much more important. This is
affected by:

	- interleave supported by controller
	- data buffering in controller
	- head switch time of drive
	- track-to-track seek time of drive
	- drive data format (MFM, RLL, ESDI, SCSI in increasing speed order).

If you deal with lots of short accesses to widely varying data areas (e.g.
random lookups in a database with thousands of short records), then the
seek time will be important. For everything else, including program load
time, sequential data search, etc., the data rate is much more important.

CONTROLLERS

Your absolute fastest possible data rate will be had with a synchronous
SCSI controller running at full speed with a SCSI drive. I haven't seen one
yet.

Next is an ESDI controller/drive running full speed. CAST makes controllers
that run full speed (> 1 MB/sec on Coretest!); Adaptec is supposed to (I'm
testing that later this week). OMTI controllers do not get full performance
out of ESDI: they 'only' go around 700K/sec. I haven't tried the WD ESDI
controllers, but if their MFM/RLL performance is any indications, I doubt
they would do very well.

Next is RLL full speed combo. Both Adaptec and OMTI versions go full speed
1:1. Adaptec is a little faster (less overhead/better buffering) under
most circumstances. If you have a very fast bus (10MHz 0 wait state) though,
the Adaptec controllers actually slow down! If you have a slow AT, the
Adaptec is definitely best: it gets full RLL speed (> 700K/sec on Coretest)
on 6-8 MHz AT's. OMTI gets 660-700K/sec on 8+ MHz AT's.

MFM running 1:1 interleave is next, getting about 1/3 less throughput than
RLL (around 450K/sec). Adaptec and OMTI make good MFM controllers. Certain
WD flavors can do 1:1. DTC controllers don't.

If a controller can't handle 1:1 interleave, you lose big very quickly. 2:1
interleave cuts your data rate in HALF! (There's no such thing as 1.5:1).

DRIVES

The only really tricky question is: "Which drives are good RLL drives?"

(Well, a second part is 'which controllers can do RLL best on non-RLL
	drives?' Answer: Adaptec has better window margins (see #1 below
	for definition) than others. Not a big deal in general, though.)

The answers:

	1) The Seagate ST-225 and ST-238 are *NOT* good for RLL. They are
		barely good as MFM drives! (Their electronics and platter
		material just can't handle the narrow 'window margins'
		(technical term meaning 'how accurate must the data signal
		timing be?').

	2) Miniscribe drives, whether certified for RLL or not, make prettty
		good RLL drives. Their electronics/platters were *designed*
		for RLL. Some are not officially RLL certified, which simply
		saves Miniscribe from some warranty claim costs. 3650's work
		just fine!

	3) Maxtor drives seem to work just great, even though they are not
		certified. Also note that the 1140 is really a 2190 with a
		different label: It is advertised as having only 918 cylinders,
		but really has 1224. $1795 at Fry's + an RLL controller gets
		you 240MB of disk space!

	4) Anybody have experience with other brands?

Pete

-- 
  OOO   __| ___      Peter Holzmann, Octopus Enterprises
 OOOOOOO___/ _______ USPS: 19611 La Mar Court, Cupertino, CA 95014
  OOOOO \___/        UUCP: {hpda,pyramid}!octopus!pete
___| \_____          Phone: 408/996-7746