I've also found that many of the SCSI disks we use around here report
that they are having trouble reading bad sectors, but that they do *NOT*
automatically remap them to new sectors.  Using SunOS's format utility to
remap them or Jason Torp's sdremap program to remap them under NetBSD has
proven to be quite successful at breathing new life into disks for several
years.  If we see  a lot of errors on a disk, we know it's pretty much
toast.  However, if we get a few persistently bad sectors, a remap usually
fixes things up quite nicely.

Hope this helps.
-Brian

On Aug 20,  1:33pm, Frederick Bruckman wrote:
} Subject: Re: Of SCSI disks and media errors
} On Wed, 19 Aug 1998, Eric S. Hvozda wrote:
} 
} > I've got some SCSI disks here that recently have begun to report
} > "Media Error".
} > 
} > I was under the impression that "modern" SCSI disks don't report
} > media errors until their spare sectores are exhausted.  Is this true?
} 
} AFAIK, If a drive is set up to replace bad blocks automatically (on read),
} it will replace the bad block with a blank one. The data will be lost.
} It has to report this to the user somehow, so you get a "media error" on
} every read. After a succesful write to the (substitute) sector, the error
} goes away.
} 
} I've verified this on SyQuest type drives on NetBSD, with SCSI_VERBOSE set
} in the kernel options. That particular cartridge didn't last long,
} however.
} 
} > Or can I breath new life (and lose the media errors) by doing a low
} > level format on the disk or is it at the end of its useful life?
} 
} Typically, a "modern" drive (SCSI, >500MB) doesn't find any new bad blocks
} unless is has serious mechanical problems. An older ESDI might find a
} couple of bad sectors and go on for many more years; a 3-1/2 SCSI often
} fails the low-level format, and then you know for sure that it's unusable.
} As long as you're prepared to throw it out anyway, it can't hurt to try.
} All things considered, I'd give it about a 50-50 chance. ;)
} 
>-- End of excerpt from Frederick Bruckman