Date: Sat, 30 May 1998 18:57:41 +0930 From: Greg Lehey <grog@lemis.com> To: walton@nordicdms.com, freebsd-questions@FreeBSD.ORG Subject: Re: fdisk slice oddities Message-ID: <19980530185741.K20360@freebie.lemis.com> In-Reply-To: <19980530073409264.AAA277@mail.nordicdms.com>; from Dave Walton on Sat, May 30, 1998 at 12:34:09AM %2B0000 References: <199805140024440448.02FAF632@mailgate.execpc.com> <19980530073409264.AAA277@mail.nordicdms.com>
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On Sat, 30 May 1998 at 0:34:09 +0000, Dave Walton wrote:
> I was just setting up a new 2.2.6R system, and saw something odd
> in fdisk that I haven't noticed before. I'm hoping one of
> you can explain this to me. ("fdisk" refers to the interactive
> version in sysinstall, not the other one that I don't know how to
> use.)
>
> When I go into fdisk, it reports the disk geometry as detected during
> boot: 4960/16/63
> If I tell it to use the whole disk, it keeps that geometry and makes
> the necessary slices. But if I tell it to use the whole disk in
> dangerously dedicated mode, it changes the geometry to 311/255/63.
Dedicated mode. It's not only not dangerous, it's safer than
non-dedicated mode.
> Is there some particular reason why dangerously dedicated mode
> changes the drive geometry?
It might come closer to getting it right.
We need to completely revise this stuff. Nobody has really looked at
it for as long as I've been involved with FreeBSD (about 4 years). In
that time, computers have come to accept large disks, we have various
mapping models for Microsoft, and we (FreeBSD) need to have tools
which can handle the changed situation.
I suppose the most important difference is that no modern disks have a
rigid geometry any more (in other words, the terms cylinders, heads
and sectors are all faked). All we care about is the LBA (logical
block addressing) mode. FreeBSD has been doing this for a long time,
but we've still been inventing fake geometries for the sake of other
systems. It's about time we stopped, but I, for one, don't know what
kludges Microsoft has applied. In dedicated mode, this shouldn't make
any difference, but if you want to share, there could be problems.
Apart from the observation, did you have any problems?
Greg
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