UNIXpc crash & can't restore cpio - HELP! (long)

[Charles A. Sefranek]

In article <588 at holin.ATT.COM> doc at holin.ATT.COM (David Mundhenk) writes:
>
> ...                      Then I tried to restore 
>my cpio backup (saved with cpio -ocvumB>/dev/rfp021
>on 10 sector floppies). On disk #3, I got the message:
>
>"I/O failure on header: I/O error
>Can't read input; aborting."
> ...

>
>W H A T   G I V E S ?
>
>This is the first time I've had trouble with a cpio backup on this 
>system. Could it be a bad floppy, are my heads dirty, or what?
>

I ran into this problem too!  It drove me nuts until I finally found out
what was going on.  I remember other people on the net complaining about
this too, usually blaming cpio.  I should have suspected something when I
bought a BIG batch of those cheap floppies and hardly ever found a bad one...

If you format floppies with the ua (and even if you don't) BE CAREFUL - the
"surface test" it runs DOESN'T ALWAYS FIND BAD FLOPPIES!!!  Even using iv
won't find them.  The only reliable method I've found is to use iv with
the -l option to force 10 passes of the surface test.  This takes a LONG
time but its worth it.  The command to use is:

     iv -iwl /dev/rfp020 descriptionfile

(See the manual for descriptionfile).  Naturally you have to follow this
with the appropriate mkfs command if you want to put a file system on it
(not necessary for cpio diskettes).

After I discovered this, I wrote my own shell script to format floppies
and guess what -- I found LOTS of previously "good" floppies that are actually
bad.  I went through all my backups weeding them out.

Keep an eye on the /usr/adm/unix.log file when you are formatting floppies.
If you format a floppy that has never been formatted before you should
typically get four entries for it.  If you reformat a previously good
floppy, you should get NO entries.  If you get entries for a previously
formatted floppy, and it appears to format OK, then it encountered soft
errors during the formatting - I would put it aside and only use it for
non-critical info.  The system will automatically delete the unix.log
file if it gets too big (somewhere around 10K bytes).

Oh, by the way, if you understand how to create the descriptionfile per the
manual above, you can format floppies with 10 sectors per track, and 42
cylinders; that's right 42 cylinders, not just 40!!!  This gives me an extra
40 blocks on each floppy.  Can't guarantee it'll work on everybody's drives, 
but I know at least two other people who do the same.  (Don't try for 43 
cylinders, the drive makes an awful crunch when it hits the stops!)

--
 Charlie Sefranek	cals at cals01.NEWPORT.RI.US
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