386/ix VTOC 'support'

Leigh Clayton loc at tmsoft.UUCP
Sun Aug 5 00:35:58 AEST 1990


 I have a Magneto-Optical disk, which forces me to deal an a daily basis
with the grisly details of 386/ix VTOC processing (the things 'labelit'
writes).

 My guess as to the rules actually used by 386/ix is as follows:

1/  If I edit /etc/partitions to a correct value, and try to mount a
    file system that has an incorrect VTOC entry, mount does a careful
    check on the VTOC data, sees that they're wrong, and ignores the data
    in /etc/partitions.

2/  If the on-disk VTOC data is correct, mount writes whatever is in
    /etc/partitions over it (utterly no validation here).

  I won't go into the opinion I have of these rules (I expect you can guess),
but I wonder if anyone can definitely verify that this is the way it works,
and even better, suggest a way to fix up the VTOC when it's been clobbered
(which seems destined to happen at least weekly for the rest of the time
I run 386/ix).

 In case you care, the fundamental problem is that the MO media can be changed,
they're like floppies with 290 meg on each (:-) except that you *never* get
real disk errors (data good for 15-20 years :-) :-). The only way I have been
able to get them 'supported' by 386/ix, however, is to basically put a little
file system on each one in a fixed location, and keep /etc/partitions data
in a file in this little file system. I then use a script to mount a MO disk
that makes a new /etc/partitions from a fixed stub plus this data, before I
do any mounts. Sounds good, but in practise I keep losing VTOC entries on the
MO disks. If I could figure out a reasonable way to rebuild them, this would
be OK (well, I could deal with it).

 By the way, I'm relatively new to  Unix (only a year or so), so don't decline
to suggest something because it's so simple I must have tried it - I very well
may not have.

-----------------------------------------------------------
loc at tmsoft.UUCP   (Leigh Clayton)   uunet!mnetor!tmsoft!loc



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