Date: Wed, 31 Jul 2002 16:41:50 +0200 From: "Siegbert Baude" <Siegbert.Baude@gmx.de> To: "robert Backhaus" <robbakfreebsd@yahoo.co.uk>, "Peter Leftwich" <Hostmaster@Video2Video.Com> Cc: "Cherie & John Carri" <cjcarri@earthlink.net>, "FreeBSD LIST" <FreeBSD-Questions@freebsd.org> Subject: Re: Can FreeBSD make a hard drive unbootable by other OS's ? Message-ID: <002201c238a0$67c546e0$406a3c86@whwurm.uniulm.de> References: <20020731013439.8264.qmail@web12903.mail.yahoo.com>
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Hi, Cite from the FAQ: > > "The advantages of this mode are: FreeBSD owns the > > entire disk, [snip] > > In ``dangerously dedicated'' mode, the BSD bootstrap > > starts at sector 0, and > > this one is the only sector that always translates > > into the same C/H/S > > values, regardless of which `translation' your BIOS > > is using for your disk. > > Thus, you can also swap disks between > > systems/controllers that use a > > different translation scheme, without risking that > > they won't boot anymore." End of cite > > It isn't clear but they seem to be "selling" the > > reader on this version, > > even though the misnomer and scary name has the word > > dangerous in it. > > > > Er, that was kind of question one. > > Now we've got 40GB disks for the price of a good day's > work, those tracks are rather unimportant. I still > would use DD mode if I didn't want to dual boot, > knowing that any strange formatting can be zapped away > fairly easily. This was discussed in-depth on this list (or maybe stable?) when the option to format a DD-disk was hidden in sysinstall. You still can, but it is deprecated, because (at least several) modern BIOSes really want to have a PC-style MBR and refuse to work otherwise. So don't do, except you really know what you're doing. > > "To return a ``dangerously dedicated'' disk for > > normal PC use, there are > > basically two options. The first is, you write > > enough NULL bytes over the > > MBR to make any subsequent installation believe this > > to be a blank disk. > > You can do this for example with `dd if=/dev/zero > > of=/dev/rsd0 count=15`" Personally I would recommend: dd if=/dev/zero of=/dev/rsd0 bs=512 count=1 as this really erases the complete block. If you don`t have SCSI it's "ad" instead of "sd", of course. > > Question 3, is this fdisk /mbr a DOS command or a > > FreeBSD command, or both? > > > > Dos command. It's the dos disk partitioner. Great for > this, but it's too slow for most PC installers, who > use things from Ontrack that format a disk in about 5 > seconds. Just fdisk /mbr will be finished in a few seconds. As fdisk is only able to format FAT its speed is irrelevant for FreBSD or Linux (but you're right, it's horribly slow on huge disks). Ciao Siegbert To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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