> >> But we can (and IMHO probably should) do better for either signle-disk
> >> systems or for SCSI controllers, like Adaptecs, where two fields of
> >> the C/H/S geometry is fixed for all disks on a given controller.
> 
> >I don't understand that last sentence...
> 
> [disklabels snipped]
> 
> By C/H/S I meant the BIOS geometry -- which AFAIK is fixed, at least
> on old Adaptects like the 1542 or the Buslogic controllers we support.
> (A fixed C/H/S geometry is not terribly meaningful on a modern SCSI
> driver with ZBR.)
> 
> Just one more datapoint that confusion over what "Geometry"
> means is rife :).

And how. Here's another datapoint now that I've looked into it some more:

This weekend I evacuated my data drive (sd1) and let sysinst run wild.
The main no-no I found was that the BIOS geometry I give to sysinst isn't
arbitrary. I pretty much have to pick the same H/S numbers as my usual boot
drive sd0, or else booting the new installation from sd1 causes the machine
to cold-boot instead (Yow!).

Since I can't exactly reinstall sd0 right now (it has my win95 partition and
also the 1.3.2 installation I'm using to type this), I don't know if it is a
fixed 64 heads, 32 sectors (1 meg per cylinder) chosen by the BIOS or what I
happened to pick when I was originally partitioning the disks with OnTrack
Disk Manager. My controller is an aic7880 (ahc0) which is fairly new, so this
sounds like the Adaptec "all disks" rule referred to in the first quoted
paragraph above.

This all causes me to wonder if there isn't some way of diagnosing what the
BIOS thinks each disk looks like, so that we can eliminate the guesswork. I
bought The Complete FreeBSD 2nd Edition so I could check out their installer
and documentation; they determine the BIOS geometry somehow and supply it as
a default in their FDISK phase of installation. While you can change the BIOS
geometry from that program, their installation instructions don't talk about
it as it's probably a bad idea unless you really know what you're doing.

According to the trouble-shooting section, if you use a DOS partition program
to set up the disk before running the installer, they will clue into the
geometry used by the DOS partition map.

Todd Whitesel
toddpw @ best.com