I had tried reassigning the blocks, but the disk would always complain
about not being able to read a certain block even after I had reassigned
it. It was always the same block, and each error stepped up one block.

> Try reassigning the bad blocks.  E.g. if it complains about block
> 12345 on device sd0:
> 
> scsisctl /dev/rsd0c reassign 12345
> 
> --
> entropy -- it's not just a good idea, it's the second law.
>