badsect/sector numbers

[Ron Stanonik]

On the off chance that I'm not the only one confused about the
correct sector number to feed badsect (4.2bsd, for tucking bad
disk blocks out of the way when reformating is inconvenient) I
pass along my experience (with a cdc 9766 on an emulex sc21 on
a vax 780).

The badsect man page seemed clear enough, badsect the sector
number reported in the hard error message.  Wrong!

The sector number (sn#####) reported in the error message
appears to be the starting sector of the transfer, not the
sector containing the bad block.  So, when I dumped the
filesystem I got one value, and when I dd'ed I got another.
Needlessly said, I chased phamtom bad blocks for a few days.

The sector number computed from the cn/tn/sn numbers in the
error message (after subtracting the base of the filesystem
from cn) turned out to be high by 1, apparently because
the emulex sc21 automatically increments the sector register.
That ran me around a bit too.

Caveat badsector.

Ron Stanonik
stanonik at nprdc.arpa