Date: Sun, 26 Jan 1997 21:51:12 +1100 From: Bruce Evans <bde@zeta.org.au> To: freebsd-hackers@FreeBSD.ORG, j@uriah.heep.sax.de Subject: Re: fdisk headache Message-ID: <199701261051.VAA26848@godzilla.zeta.org.au>
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>> Boot selectors won't work either.
>
>Since there's nothing to select from. ;-)
>Right now, there are three reasons to still call it ``dangerously
>dedicated'':
>
>. Since the MBR is identical to the BSD bootstrap, there's no room for
> things like `nextboot' after the MBR, and you can't replace the MBR
> by fancy things like a boot selector. Hence, in a system that is
> not FreeBSD-only, you could at best make drives != #0 ``DD'', and
> you won't be able to boot select away from that drive once you
> switched there. (Normally, booteasy allows to wander around back
> and forth through all the drives.)
There may be 512(*) sd drives, 512 od drives, 16 cd drives and a small
number of wd and fd drives :-). That's a lot to select from.
(*) Actually at most 128(**) floppy drives and 128(**) hard drives
altogether (because of the BIOS interface limit).
(**) Your BIOS may vary.
>. Some operating systems might choke on that fdisk table afterwards,
> so if you are going to install something else on such a drive later,
> it's best do do a ``dd if=/dev/zero of=/dev/rXXX count=100'' before
^^^^^^^^^
> recycling the drive to another task.
Should be count=1. If 1 won't work, then 100 may not be enough either,
and you'd better know what you are doing. E.g., if there is a FreeBSD
slice at offset 100000, then there will be a BSD label at offset 100001,
and it should be zeroed to prevent it being resurrected if a BSD slice
is created at offset 100000 a year later and the label hasn't been
changed.
>The plus side is:
>...
>. The number of BIOS geometry constraints to care for reduces drastic-
> ally, so you can usually (*) ignore any geometry issues.
>
> (*) I.e., the BIOS's geometry idea involves at least 15 sectors per
> track, 4 heads, and the root file system is not larger than 30 MB.
Actually if the root file system is below cylinder 1024 in the BIOS
translation mode. I think the 15 sectors/track limit only applies for
floppies.
Bruce
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