How to translate from f/s block # to absolute disk sector?

[James P. H. Fuller]

     A bad spot has appeared in my /usr2 file system and I'm very unclear what
to do about it.  (I'm running ISC release 2.2.) 

If I try to mount the offending filesystem,

   # mount /dev/dsk/0s4 /usr2

the disk spins for a while and then mount tells me "free block read error on
Primary AT Hard Disk unit 0 partition 4.... cannot mount /dev/dsk/0s4."

If I try to check/repair the filesystem,

   # fsck /dev/dsk/0s4

then during Phase 5 - Check Free List fsck responds "CAN NOT READ: BLK 106626".
If I tell it to continue and salvage the free list it seems to do so, i.e. fsck
goes to completion, tells me the file system was modified, and gives me back
the root # prompt.  However, the error is still there and the file system is
still not mountable.

If I make a new filesystem for /usr2 and restore from my backups it will then
be mountable and will run fine -- until the next time I reboot.  Then the same
old error reappears and the filesystem isn't mountable.


     The thing it *seems* I ought to do is to add information about this bad
disk spot to the list of bad sectors in /etc/partitions and *then* make a new
filesystem, but (HERE'S THE MAIN PROBLEM I'M ASKING ABOUT) the data in
/etc/partitions is in the form of absolute sectors, but what fsck reports is a
block number in a certain file system, and I don't know how to go from the one
to the other.
     I tried using ISC's sysadm program to add the bad block info.  This looks
promising, since choice 1) under the HARD DISK MANAGEMENT submenu is

   1) addbadblocks   enter bad sector information

but in fact the prompts you get if you choose addbadblocks don't have anything
to do with blocks -- sysadm wants absolute sector number, and no backtalk!
(Infuriatingly, if you hit ? to get help when it prompts for the absolute
sector number, it responds

   "This is the absolute sector number that was printed on the console."

although what was printed to the console was NOT absolute sector number but
rather relative (to a certain f/s) block number.)

     In hopes that the bad area might be identified differently if I used
sysadm to check the bad f/s I tried choice 3) on the same menu, checkhdfsys.
It turns out this looks for file systems that are mounted, unmounts them and
checks them.  There's no way to tell it to check a f/s that *isn't* mounted.
So it seems that the only info available to me is what I get by running fsck
from the command line.

     I read and read in TFM and elsewhere, but not to much purpose.  I did
find a sentence in the man pages for fsdb that says "[fsdb] has conversions
to translate block and inode numbers into their corresponding disk addresses"
but the rest of the entry for fsdb is pretty cryptic (I mean it might as well
be written in Hittite, as far as I'm concerned) and I can't figure out how to
get it to do this, or even if it *can* do the conversion *and report it* to the
console, instead of just doing it internally for its own purposes.
 
     
     Will some kind and knowledgeable soul please tell me how to calculate an
absolute sector number from a block number, or how to persuade fsdb to do this?

                                           THANKS VERY MUCH
                                               James Fuller
                                     jim%crom2 at nstar.rn.com