Date: Wed, 23 Aug 95 11:43:43 MDT From: terry@cs.weber.edu (Terry Lambert) To: bde@zeta.org.au (Bruce Evans) Cc: bde@zeta.org.au, freebsd-hackers@freebsd.org, imb@scgt.oz.au, msmith@atrad.adelaide.edu.au, roberto@keltia.frmug.fr.net Subject: Re: Install issues (was: State of the union speech Message-ID: <9508231743.AA04656@cs.weber.edu> In-Reply-To: <199508230234.MAA31690@godzilla.zeta.org.au> from "Bruce Evans" at Aug 23, 95 12:34:27 pm
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> Physically it is 36 but the controller should report 35...unless this > form of translation is regarded as a bug fix for the option base 1 > sector numbers :-). What happens if translation is enabled and the set > parameters command tells the drive that there are 36 sectors/ track? > Translation has to slip a sector for each track if translation is to > work. I guess the spare sectors should be inaccessible in translated > mode (you could specify sector 0, but the accumulated slippages stops > that from being related to a physical sector 0). The spare sectors are inaccessable in translated mode. They are also inaccessable (give an error) in non-translated mode IF the drive was not low level formated not in translated mode. > >The sparing doesn't actually go off unless you also disable translation. > > Yes it does. Of course you have to add 1 to the number of sectors in > the BIOS geometry and in disk labels to use the extra sectors. Think about this for a second. The BSD driver uses "LBA" -- or what the rest of the world has called absolute sector addressing before the DOS weenies started to pollute the world with their own vocabulary. Basically, that means that as I linearly traverse the drive space, every 36th sector is just... not there. > This can be handled by using adjusting the geometry in the smart driver. > Use a drive table entry with 35 sectors since 35 is all the BIOS can > normally see. Use 36 sectors in the smart driver. Other OS's will have > problems reading file systems written by the smart driver. The smart driver has to use geometry itself to translate logical absolute sectors to physical absolute sectors -- skipping the missing "36th" sector for each set of sectors. This is more information that a driver really want to have to know, and it may actually be impossible to provide. > I think all the BSDs used the disklabel values until I "improved" the > FreeBSD driver in 2.0.5. This is what the disklabel was for - for > specifying the final values to be used in case the hardware or BIOS > values are unavailable or wrong. The hardware values are wrong, and no matter what disklabel values you specify, they'll be wrong too, since as soon as I try to read the sector at offset 35 (option base 0) using the BSD driver, I'm going to get an error unless the driver (not the controller) translates this into a request for the physical sector at offset 36 (option base 0) and reduces the overall apparent drive size by 1/36th. The question now is how to make the driver do this. I don't think it's possible without a lot more crap than we want (or can fit) in the boot code. The answer is to reset the jumpers and reformat the drive, so it isn't necessary. Or only use BIOS calls, which isn't currently an option. Terry Lambert terry@cs.weber.edu --- Any opinions in this posting are my own and not those of my present or previous employers.
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