Re: My SCSI HD has 34 heads, not 255...

Andries.Brouwer@cwi.nl
Sun, 16 Jun 1996 13:33:52 +0200


Thomas E Zerucha:

: All true, but fdisk and lilo are making the call and complain or give
: strange results when the number returned by the call disagrees with
: reality.

Ah, but I just said that there is no reality.
Thus, it is impossible to disagree with reality.
A SCSI disk is addressed in terms of logical block number,
not in terms of cylinders, heads and sectors.

Thus, in principle every OS and every controller is free to
invent numbers of cylinders, heads and sectors, just as it likes.

Linux will ask the controller about the geometry it has invented
or invent something itself. There can never be any guarantee
to be `right'. But when you have several operating systems
on the same disk, or if you use the same disk on several
controllers, you may have to invent your own reality and tell
all systems that differ explicitly about your choice.

That is why you can give lilo and fdisk explicit CHS information.

If you have an explicit proposal on how to make fdisk do the right
thing more often - i.e., look at the partition table and guess
what disk geometry you would like to go with that - then such
sugestions are welcome.

: > Hmm. For fdisk 3.04:

: I have 2.1. Apparently RedHat is slightly behind. The problem originally
: surfaced a few months ago.

No, fdisk (currently fdisk 2.1) and fdisk3 (currently fdisk 3.04) are
rather different programs. The latter does not (yet) supersede the former.
Both have their uses.

Andries