Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!amdcad!ames!hao!gatech!bloom-beacon!mit-eddie!apollo!rees
From: rees@apollo.uucp (Jim Rees)
Newsgroups: comp.sys.apollo
Subject: Re:  DSP90/MSD-500 Disk Errors
Message-ID: <3a5be7ef.b8ab@apollo.uucp>
Date: 18 Feb 88 16:02:00 GMT
References: <8802160311.AA20797@caen.engin.umich.edu>
Organization: Apollo Computer, Chelmsford, Mass.
Lines: 15

Note that "disk block header error" usually means that the block was read
OK, but had funky stuff in the block header.  This does not imply a disk
read error, and any attempt to put the block in the badspot list will only
make things worse.

The block header is an extra thing stuck in front of the data that
contains useful stuff like the uid of the object that the data came
from.  In theory this makes it easier to salvage the disk if something
goes wrong.  I think this idea came from Parc, where it was used in
the Alto file systems.

There are various programs in /systest/ssr_util (rwvol, fixvol) that
can read and display block headers.  But take the warnings seriously --
you can screw up your disk with these if you don't know what you're
doing.