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To: freebsd-questions@freebsd.org
Cc: wmoran@iowna.com
Subject: Re: SCSI bad block remapping
References: <3B327713.46173EC5@iowna.com>
From: Dale Hagglund <rdh@best.com>
Date: 04 Jul 2001 18:44:48 -0600
In-Reply-To: <3B327713.46173EC5@iowna.com> (Bill Moran's message of "Thu, 21 Jun 2001 18:37:07 -0400")
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Bill Moran <wmoran@iowna.com> writes:

> 1. (and most important) how do I make sure bad sector remapping is
> turned on for this (and all) SCSI drive

I work with some guys who've done weird things with and to scsi drives
for quite a few years, and, according to them, turning on automatic
sector remapping can have surprising and usually undesirable results.

The two key issues are

        (a) the disk might do remapping in fairly large chunks, even
        up to a track in size, and 

        (b) after remapping, the data in the remapped region is
        undefined.

Since your I/O operation probably *wasn't* a full track (or whatever
the remapped chunk turns out to be), there are now a bunch of blocks
that are undefined that the disk has never complained about.  So much
for the data integrity that your RAID1 was giving you.

Dale.

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