Date: Thu, 24 Oct 2002 18:00:30 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: mark@thuvia.demon.co.uk Cc: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/lib/libdisk Makefile chunk.c write_alpha_dis Message-ID: <20021024.180030.103860565.imp@bsdimp.com> In-Reply-To: <200210241956.g9OJuQ43046607@dotar.thuvia.org> References: <XFMail.20021024151029.jhb@FreeBSD.org> <200210241956.g9OJuQ43046607@dotar.thuvia.org>
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In message: <200210241956.g9OJuQ43046607@dotar.thuvia.org>
Mark Valentine <mark@thuvia.demon.co.uk> writes:
: > From: John Baldwin <jhb@freebsd.org>
: > Date: Thu 24 Oct, 2002
: > Subject: Re: cvs commit: src/lib/libdisk Makefile chunk.c write_alpha_dis
:
: > How about Adaptec SCSI BIOS's and other "smart" BIOS's that look
: > at the MBR to guess what geometry you are using so that they can
: > adjust their BIOS to DTRT? These choke if you don't have a valid
: > MBR. MBR's are part of the i386 defacto architecture, deal.
:
: Don't these BIOSs have fallbacks for the case where there's no DOS-style
: MBR partition table? The PC BIOS copes with it for IDE disks using the
: disk type stuff or whatever; it should be no different for a SCSI BIOS.
should be != reality. I have some aha scsi controllers that seem to
get really cranky when you don't have an MBR on the disk and the BIOS
is enabled for them.
: As I said, if that's broken and you *really* need the MBR partitioning
: table as a crutch, it's important not to force that to affect the user-
: visible partition labelling scheme for the common case of one BSD disklabel
: per disk.
On the pc architecture you are requires to have a MBR. This is a
non-optional part of the 'de-facto' spec. All FreeBSD labeled disks
have a MBR on them, even the DD ones. With DD mode, the MBR is bogus
in that it doesn't describe the actual hardware. We've been through
this about a dozen times now in various forums.
The problem here is one of historical usage. /dev/ad0a has worked on
FreeBSD since 0.0 and back into the 4.[34] BSD past before that.
Warner
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