Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!blake!corey
From: corey@blake.acs.washington.edu (Corey Satten)
Newsgroups: comp.sys.next
Subject: fixing bad superblocks
Keywords: NeXT bad block optical disk
Message-ID: <1208@blake.acs.washington.edu>
Date: 13 Mar 89 23:02:00 GMT
Organization: Univ of Washington, Seattle
Lines: 37

Fixing trashed optical disk superblocks on NeXT 0.8.

I have just fixed the 3rd (on campus) trashed superblock on a NeXT
optical disk.  My current hypothesis is that shutting down via the
power button instead of running /etc/halt is the cause.  Fortunately,
it seems that the solution is relatively painless if you can put the
optical disk in a machine which is either booted off a hard disk or
booted diskless off another cube.

First, verify that your problem is really a bad superblock by typing as
root:

	/etc/fsck -n /dev/rod0a

It will say something about not being able to read block 8.  Then fix
it by:

	/etc/fsck -b 16 /dev/rod0a

This rebuilds the file system (and restores the "bad" superblock) from
information in one of many alternate copies of the superblock which the
designers of the Berkeley fast-filesystem thoughtfully included.  Note,
the NeXT 0.8 manpage for fsck is incorrect:  block 32 is *not* an
alternate superblock.  Two other suitable alternates are: 848 and 1680.

Note:  even though the error messages might lead you to believe there
is an actual problem with the optical medium, I believe this is not the
case and the disks I have restored show no sign of further trouble.

Corey Satten
corey@cac.washington.edu

P.S.  The above posting is for the convenience of the network community.
It is not a "comment" on NeXT quality.  In my experience NeXTs are very
well behaved.  The two I use every day have not crashed in recent memory
(~2 months).  Quite impressive for an initial pre-release!  Sure, I've
sent in bugs and suggestions.  What else is new?