Xref: utzoo comp.sys.ibm.pc:18107 comp.binaries.ibm.pc.d:757
Path: utzoo!attcan!uunet!husc6!rutgers!ucsd!ames!vsi1!octopus!pete
From: pete@octopus.UUCP (Pete Holzmann)
Newsgroups: comp.sys.ibm.pc,comp.binaries.ibm.pc.d
Subject: Re: Steve Gibson's "SpinRite" product
Summary: Some answers, plus explanation of why PD versions may not be safe
Keywords: Non-destructive low-level format; interleave optimization
Message-ID: <314@octopus.UUCP>
Date: 16 Aug 88 17:47:17 GMT
References: <989@acornrc.UUCP> <246@humming.UUCP>
Reply-To: pete@octopus.UUCP (Pete Holzmann)
Distribution: na
Organization: Octopus Enterprises, Cupertino CA
Lines: 76

This article resolves some misconceptions presented in a couple of articles
posted about SpinRite. I've used it, and understand what it does pretty
well, so I'll attempt to clear things up:

In article <246@humming.UUCP> simcha@humming.UUCP (Simcha Lerner) writes:
>In article <989@acornrc.UUCP> bob@acornrc.UUCP (Bob Weissman) writes:
>>Having run the recently posted "spintest" program, it appears that my
>>Seagate ST238-R has been formatted with a suboptimal interleave factor
>>of 4.  ("spintest" claimed it took 18 revs to read a track! Bleah!)
>
>This figure is hard to believe, since the theoretical worst case for
>normal MFM hard drives is 17 rotations.  (Unless it is counting the
>1/2 rotation (on average) latency to find the first sector.)

An ST-238 (or almost any other "30 MB drive") is really a 20MB
drive running with an RLL controller. Therefore, it has around 26 sectors.
I've actually seen an ST-238 take 28 rotations to read a full track. It
just means that the interleave is optimally bad, and the controller is
getting confused every once in a while on top of it all. With a well-
implemented controller, it is true that the worst you could get is N
rotations (1 rotation per sector).

>>"SpinRite" claims it can perform a non-destructive low-level format
>>while optimizing interleave.

>[Mentions Phoenix version that does this at setup time]
>[Craig, in another article, mentioned ILEAVE16/17 and iau.exe]

The problem with most 'non-destructive' low level formatters I've seen is
that they don't do sufficient testing of the disk, and can't handle errors
that are found if they do perform testing.

This isn't something to worry about if you are working with an unused disk,
since you have no data to lose. It also isn't particularly worrisome if your
disk has been low-level formatted recently, because the problems I'm about
to mention are mostly due to long-term changes that occur after low-level
reformatting.

One of the trickiest problems to deal with is that over time, disk head
alignment can change slightly (the head is no longer centered over the track).
If this shift gets bad enough, you will see lots of bad sectors showing up.
Low-level reformatting fixes the problem, since it rewrites the sector header
information, thus putting all the data back under the center of the head.

The trouble occurs when there's a defect that used to be just far enough off
the original track alignment that it didn't show up in original disk testing,
but that *will* be a problem after the track is reformatted. If the 
reformatter doesn't know what to do with the data if a bad sector is found
while reformatting, you will be in trouble. Avoiding existing marked bad
sectors is a nice idea, but doesn't take care of this problem.

Other than the interleave optimization, the nicest thing about SpinRite is
that it does extensive surface testing. And it knows enough about bad
sectors that it can move data to a good spot on the disk. AND, it can return
sectors previously marked 'bad' to normal use, if the defect is no longer
a problem.

While I'm on a roll, perhaps I should mention some examples of why sectors
marked 'bad' are probably not really bad after all:

	1) Most common reason for 'bad sector' is that the head is off-track
		and the sector header can't be read. New low level format
		solves this problem completely.

	2) If a defect is actually in the space between sectors on a track,
		there's no reason to mark a sector bad.

	3) If a defect was in the center of the track before, and the heads
		have shifted, it may not affect the track any more.

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