I guess no one writes them down!

If the first alternate (block 32) is invalid it all gets hard.
Actually a good bet would be to run the same version of newfs
as created the filesystem, specify -N and try the resultant numbers.

Since newfs no longer creates cylinder groups on cylinder boundaries
you can't even look at the 32nd block of every cylinder any more.

Could be worth ditching the output, maybe unless -N is specified.

Does anything expect to see (or ever write to) the alternate superblocks?
If not the number could be reduced somewhat.

	David

-- 
David Laight: david@l8s.co.uk