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From: jca@pnet01.cts.com (John C. Archambeau)
Newsgroups: comp.sys.ibm.pc
Subject: Re: MFM as an RLL drive?
Message-ID: <906@crash.cts.com>
Date: 15 Dec 89 07:16:02 GMT
Sender: root@crash.cts.com
Organization: People-Net [pnet01], El Cajon CA
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phil@diablo.amd.com (Phil Ngai) writes:
>Please stop repeating these untruths. Formatting an MFM drive as RLL
>will not physically hurt it. It may not work in RLL mode but then,
>some disks sold as RLL don't work in RLL mode either. In fact, some
>disks sold as MFM don't work in MFM either. (I'm referring to DOAs.)
>
>RLL was designed to be used with MFM media by using the flux changes
>more efficiently, not by forcing more flux changes in. The only thing
>RLL requires is tighter timing than MFM. If the drive delivers a lot
>of jitter, RLL may not work but you can always revert to MFM, if you
>have a system that can perform the low level format. I have heard that
>a few systems can not do this, perhaps this is where the rumor that
>using an MFM drive as RLL will break it came from, but most systems
>these days can handle the reformat. 

I've encountered enough drives that won't handle the reformat.  Again, the
primary offenders were the ST225 and ST251.  I don't know exactly why (and
never knew since Seagate refused to touch them) they died, but I suspect that
they were on the low end of the quality control spectrum.  I asked the Seagate
engineer this, "If they were only formatted MFM, would you swap them without
any question?"  His answer was "Yes."  You tell me, in principle you are
probably right, but I apply a set of dead ST225's and ST251's to my reasoning,
you can theorize and state the engineering facts about MFM or RLL, but they
don't mean crap when you have seen drives killed by RLL formatting.  It may
defy how a RLL works, but then again, by your reasoning those dead drives
should reformat, but they didn't and I tried OMTI, WD, and Adaptec controllers
to bring them back from the dead (and my track record in data recovery and
hard drive restoration is noted by my customers and business associates in the
field), I agree that those drives SHOULD be working, but they didn't and never
will.  I probably encouered the exceptions to the rule, but those exceptions
have made me a stubborn believer with respect to Seagate drives.
 
     // JCA

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