Corrupt File System (was Re: Unmountable disk partitions)

[Jonathan Groves]

I posted this article in comp.unix.internals, but since then
2 other twin Vax Server 3600 have had the exact same error in the
same partition (/dev/ra0f).

Last Friday we experienced a 1/2 minute black/brown out,
with a power surge.  We expect this is our culprit,
but why that particular cylinder?  Is this a resting position
for the head, and when it powered back up zapped the disk?

I hope someone here may be able to help me.  Thanx.

JG> Today one of our file servers crashed [Ultrix] and
JG> when it tried to come back up, it failed during the fsck.
JG> 
JG> After an interactive session with fsck, the disk still
JG> failed, and another interactive fsck leaves me with this:
JG> (Comments from M.K.McKusick's FSCK document (1983),
JG> included with Ultrix Supplementary Docs. Volume 3)
JG> 
JG> ** /dev/ra0f
JG> ** Last Mounted on /usr/users
JG> ** Phase 1 - Check Blocks and Sizes
JG> CG 0: BAD MAGIC NUMBER
JG> 1763713056 BAD I=28
JG> [Several of these]
JG> 1601463663 BAD I=28
JG> EXCESSIVE BAD BLKS I=28
JG> CONTINUE? y
JG> 
JG> # CG c: BAD MAGIC NUMBER
JG> # The magic number of cylinder group c is wrong.
JG> # This usually indicates that the cylinder group maps have
JG> # been destroyed.  When running manually the cylinder group
JG> # is marked as needing to be reconstructed.
JG> 
JG> ? How is the map reconstructed, and at what phase of fsck?
JG> ? Obviously after where it dies on me.
JG> ? Is this happening because I "corrected" part of the
JG> ? file system that I shouldn't have?
JG> 
JG> ** Phase 2 - Check Pathnames
JG> ROOT INODE UNALLOCATED. TERMINATING.
JG> 
JG> # ROOT INODE UNALLOCATED. TERMINATING.
JG> # The root node (usually inode number 2) has no allocate mode bits.
JG> # This should never happen.  The program will terminate.
JG> 
JG> ? So what do I do? 
JG> ? I newfs/mkfs and restore from backups...
JG> ? Is there any way I could have "repaired" the disk using
JG> ? some kind of file system binary editor (fsdb?)?
JG> ? Where would I find such an editor?
JG> ? Where would I find info on where info is stored on
JG> ? the disk and in what format?
JG> 
JG> In several places the document concludes the solution to be
JG> "See a guru."  But there's no guru index.  :-)
JG> 
JG> I hope someone out there can answer these questions...
JG> 
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