🚀 go-pugleaf

We've just purchased three Seagate 2.9G drives and I am currently
in the process of setting up filesystem on them. I want to squeeze
as much space out of the drives as possible, so I've been playing
with various disk geometries in the format program. The total
capacity of the disk is 5688447 sectors, so my approach is to
come up with come combination of cylinders/heads/sectors per track
to come as close to this value as possible. Format also requires
that you specify at least 2 spare cylinders for bad sector mapping,
so I've taken that into consideration as well.

I tried the obvious one first, using 80 sectors per track since
that seems to be very common. Why I'm not exactly sure. Perhaps
someone could explain this. In any case, I take the 80 sectors
per track and divide 5688447 by this value. Next comes the number
of heads. I've chosen 21 for this as this is the value listed
in the manual for this disk, although I'm not sure if it makes
a difference or not. So I take the result of the previous
division and come up with 3385, representing the number of
so-called cylinders. This does not work out evenly of course.
If I multiply 80x21x3385, I get 5686800, which is 1647 less
than the 5688447 sectors this disk is supposed to have. Also,
since I have to specify two cylinders as spares, in fact I
lose another 2x21x80=3360 sectors, leaving 5683440 for normal
use. Okay, that's still a lot--this *is* a big disk. However,
I thought I might be able to do better and after playing around
came up with a geometry consisting of 49 sectors per track, 21
heads, and 5528 cylinders. That gives me a total accessible
capacity of 5688312. only 135 less than the listed maximum
of 5688447. I also have to reserve two cylinders, so that's
another 2058 that cannot be used, but the end result is
only 2193 sectors are lost for spares and "round off".

My question is this: What advantage/disadvantage does one
disk geometry have over another, other than giving you more
space for real data. In my second geometry above, is the
2058 spare sectors enough? Is the 3360 in the first more
than I need? How does the disk's physical characteristics
come into play. For this disk, the manual lists that it has
2738 cylinders per head, including 2 spares, and 21 recording
heads. It also mentions that it has 6 spare sectors per cylinder
and various other figures as well. How does all this reflect
on the values I give the format program?

If anyone has an answer, I'd appreciate some advice. Thanks
very much.
-- 
Peter Steele        Unix Services Manager            peter.steele@acadiau.ca 
Acadia Univ., Wolfville, NS, Canada B0P 1X0  902-542-2201  Fax: 902-542-4364