Xref: utzoo comp.sys.ibm.pc:15644 comp.sys.misc:1433
Path: utzoo!attcan!uunet!n3dmc!johnl
From: johnl@n3dmc.UUCP (John Limpert)
Newsgroups: comp.sys.ibm.pc,comp.sys.misc
Subject: Re: RLL Technical Details (long) (was Re: RLL- why it is hard on drives)
Summary: unable to format drive
Message-ID: <338@n3dmc.UUCP>
Date: 17 May 88 12:13:07 GMT
References: <1255@kodak.UUCP> <638@mccc.UUCP> <216@octopus.UUCP> <650@mccc.UUCP> <218@octopus.UUCP> <661@mccc.UUCP>
Reply-To: johnl@n3dmc.UUCP (John Limpert)
Organization: N3DMC, Silver Spring, Maryland
Lines: 25

In article <661@mccc.UUCP> pjh@mccc.UUCP (Pete Holsberg) writes:
>Misled?  You think that the guys who told me that they were unable to
>MFM-format a plated media drive that they had run under RLL were
>kidding?  Frankly, I didn't initially believe them either, but enough of
>them said the same thing that I got rid of my ST-225 asap.  Maybe it's
>another hummingbird case: theoretically, there's nothing that an RLL
>controller can do to prevent a disk from being reformatted, but in these
>cited cases, it happened.  Probably in conjunction with a powersupply
>problem or some such thing, eh?

I think the problems with drives that can't be reformatted are caused
by destruction of servo information on drives that use the wedge
servo technique.  From previous discussions of the problem, it appears
that improper formatting with a RLL controller can overwrite the
servo section of a track.  Once this has happened, the only way to fix
the drive is to send it to a repair shop that has the special equipment
needed to rewrite the servo information.  I have heard of people
wiping out several drives in this manner.  It seems like the drive doesn't
prevent the controller from writing over the servo information.
A MFM controller might be able to do this if programmed incorrectly.

-- 
John A. Limpert
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