>  a:   1049328         0     4.2BSD   1024  8192    86   # (Cyl.    0 -  1040)

> what eactly means cpg (cylinders per group?)

It's the number of cylinders in each cylinder group, exactly what it
sounds like.  If you care what cylinder groups are, read up on FFS....

> does this number has any real importance or can I modify it from 86
> to 16?  Will it have inpact on performance?

You can change it freely in the disklabel; it won't help anything, but
won't break anything, at least not immediately.  What *does* affect
things is the value that was used when your filesystems were created.
newfs tends to rewrite the disklabel with the value it uses, which is
probably what set it that way.  (I'm not sure where disklabel gets it
from by default; I know there's a command-line option to override it,
which I usually use.)

> should I leave it 86 or change it ??

If you're not going to remake your filesystems, you can fiddle the
disklabel all you like and it won't change a thing.

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