Date: Tue, 24 Aug 1999 04:45:21 +1000 From: Bruce Evans <bde@zeta.org.au> To: imp@village.org, phk@critter.freebsd.dk Cc: cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org Subject: Re: cvs commit: src/sbin/i386/fdisk fdisk.8 fdisk.c Message-ID: <199908231845.EAA01679@godzilla.zeta.org.au>
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>Last time I tried to do this, I ran into the problem that I could not >find out the disks' geometry. At least what the BIOS thought the >geometry was so that it would acutally create a bootable disk. >FreeBSD lies for at least the UltraStor controllers because they >reported what the disk said it was, rather than the "translated" >numbers that the 34F used (and it was not possible, when last I >looked, to disable this translation). SCSI disks and controllers don't "use" any geometry. FreeBSD begins with the geometry reported by the drives. For SCSI disks, I think this still usually has something to do with the actually geometry (#cylinders and #tracks are correct, and #sectors is the average), but this geometry is normally neither useful nor used. FreeBSD then reads the partition tables and attempts to determine the geometry being used. This of course fails for disks without partitions tables, so for new disks you usually have to type in the geometry that the BIOS will use. IIRC, the U34F normally reports a geometry of 64 tracks and 32 sectors, and isn't very flexible (I vaguely remember a 128 track mode). This works OK for those huge 600 MB drives that we had a few years ago when U34Fs were almost worth using, but runs into 1024-cylinder problems for >= 1GB drives. Similar problems occur for IDE drives. The main difference is that the geometry reported by the drive is also fake, and it used to be possible to fake it in such a way that it was usable by BIOSes, and BIOSes used it. This was "fixed" when IDE drives became larger than 8.4GB. These problems mean that "auto" on a slice can't be implemented properly without solving the old problem of mapping drives to BIOS drive numbers so that the table of BIOS geometries can be used. Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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