Date: Fri, 07 Aug 1998 19:04:57 -0700 From: Mike Smith <mike@smith.net.au> To: Greg Lehey <grog@lemis.com> Cc: Bruce Evans <bde@zeta.org.au>, ks@itp.ac.ru, mike@smith.net.au, hardware@FreeBSD.ORG Subject: Re: IBM 16 GB IDE HDD Message-ID: <199808080204.TAA00473@antipodes.cdrom.com> In-Reply-To: Your message of "Fri, 07 Aug 1998 08:41:55 %2B0930." <19980807084155.H9620@freebie.lemis.com>
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> On Thursday, 6 August 1998 at 20:55:56 +1000, Bruce Evans wrote: > >>>>> how can I use the full capacity of my IBM DTTA-351680 16GB IDE drive? > >>>>> "wd" driver can see only 8GB, and manual drive geometry installation > >>>>> in fdisk did not change it - my FreeBSD-3.0-980311 can see only 8GB. > >>>> > >>>> See the 'wd' manpage for the option to use LBA addressing for disks > 8GB. > >>> > >>> There are nothing about it. > >> > >> You're obviously more out of date than I thought. From a more recent > >> wd.4: > >> 0x1000 Use LBA addressing instead of the default CHS addressing. > > > > This is seriously incomplete and out of date. LBA addressing should almost > > never be used, since no cases are known where it is necessary, and cases > > are known where it causes trashed disks (dumping to any drive where the > > default geometry is not the same as the fake LBA geometry). > > What am I missing here? I thought LBA meant "logical block > addressing". Where does "geometry" (by which I understand bogus > mapping to cylinder/head/sector values) come into it? It has to do with the fact that for legacy interoperability reasons the LBA and CHS numbers in the MBR have to match up, and the 'wd' driver still uses the CHS interface to the disk registers (lowest common denominator). The drive itself changes the mapping between the CHS register values and the LBA address based on what it thinks it's geometry is. Unless you know what it thinks it is, you can't second-guess it to get your data where you think it's going. The bootstrap CHS issue will hopefully be getting better soon; the use of the CHS interface to disks is going to be with us at least in the legacy case for some time yet. There is work underway on a replacement for the current ATA subsystem, but it really needs a sponsor. -- \\ Sometimes you're ahead, \\ Mike Smith \\ sometimes you're behind. \\ mike@smith.net.au \\ The race is long, and in the \\ msmith@freebsd.org \\ end it's only with yourself. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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