How do you derive a format.dat entry?

[Glen Dudek]

I have watched many postings go by with requests for working format.dat
entries.  I always wondered, "Why can't you just use the specifications
from the disk drive manual to write your own format.dat entry?"  Then it
was my turn.  I tried to format a Maxtor XT-8380S on a Sun 3/60.  The disk
manufacturer's manual specified 54 sectors per track, 8 heads, 1632
cylinders, and 31410 bytes per track.  I made up a format.dat entry which
looked like:

disk_type = "Maxtor XT-8380S" \
        : ctlr = MD21 : fmt_time = 3 \
        : ncyl = 1630 : acyl = 2 : pcyl = 1632 : nhead = 8 : nsect = 54 \
        : rpm = 3600 : bpt = 31410

But when I tried to run format, I got:

Block 0/0/3 - media error

After further checking, I found a format.dat entry for a Maxtor XT-8760S
in the Sun-supplied format.dat file.  According to my disk drive manual,
which also covered the XT-8760S, the geometry of the XT-8760S is identical
to the XT-8380S except that the XT-8760S has 7 more heads (and additional
platters for those heads to use).  But the Sun format.dat entry specified
only 51 sectors per track, 1626 data cylinders and 2 alternate cylinders.
This meant 3 sectors per track and 4 cylinders were missing.  When I
changed my format.dat for the XT-8380S to match these numbers, the format
ran successfully.

My question is: How do you derive a format.dat entry which will work with
the Sun format program given the physical geometry of the drive?

I tried to get an answer to this question from Sun Software Support, but I
was told they did not have this information, and could not contact Sun
engineering to find an answer to this question.  I find it incredible that
Sun Software Support is unable to talk to Sun's own engineering
department!  I am (once again) disappointed in the level of support
provided by Sun, and (once again) disappointed by Sun's lack of commitment
to their Open Systems marketing hype.

If anyone has any clues as to how the format.dat geometry information is
used by the format program, I would appreciate hearing about it.

Thanks much in advance!

	Glen Dudek
	dudek at ksr.com