kern/141992: fsck cannot repair file system in which it finds an error

[Kirk McKusick]

I am investigating your bug report about your problems with fsck
in going from 6.1 to 8.0. There have been only insignificant
changes in the filesystem during that time, so in theory you should
not have any problems going back and forth between these two
versions of FreeBSD. The fsck program has been changed to look
more critically at the cylinder group maps, so some errors that
would not previously have been detected will now be found. That 
said though, it should be able to completely fix those errors
which it appears that it is not able to do.

To help me track down your problem, please supply me with the following
information:

1) Do you have more than one 6.1 filesystem that you are running on
   this system. If so, is this the only filesystem having trouble in
   this way, or are more than one of them exhibiting similar problems?

2) Are you getting any disk errors reported for this drive in
   /var/log/messages? It really looks like there is a bad sector in
   cylinder group 48 and so even though fsck can calculate a correct
   one, it is not able to write it out. Even if errors are not being
   reported, I am inclined to write a small test program that attempts
   to read and write the affected sectors to see if the changes stick.

3) Please provide me with a `dumpfs /dev/ad4s4a'. I don't need the
   whole (huge) thing. Just the start up through cylinder group 0,
   then the output for cylinder groups 47, 48, and 49. I am looking
   for any obvious anomolies in cylinder group 48 versus its neighbors.

Hopefully we can sort out what is going wrong here.

	Kirk McKusick