Date: Thu, 23 Mar 2000 05:57:54 -0800 From: Cy Schubert - ITSD Open Systems Group <Cy.Schubert@uumail.gov.bc.ca> To: Vivek Khera <khera@kciLink.com> Cc: stable@FreeBSD.ORG Subject: Re: "dangerously dedicated" Message-ID: <200003231358.FAA01112@cwsys.cwsent.com> In-Reply-To: Your message of "Wed, 22 Mar 2000 18:30:19 EST." <14553.22411.265795.429126@onceler.kcilink.com>
next in thread | previous in thread | raw e-mail | index | archive | help
In message <14553.22411.265795.429126@onceler.kcilink.com>, Vivek Khera
writes:
> >>>>> "WL" == Warner Losh <imp@village.org> writes:
>
> WL> I didn't say that using da0a is stupid. I said using dangerously
> WL> dedicated mode is stupid. Based on the number of times I've shot
>
> I guess I don't see how to use, eg, da0a without being "dangerously
> dedicated". When I did my install of FBSD 3.3, the partitioning
> process asked if I was sharing the disk or not. I said no, so it took
> over the entire disk, but I still get the long-sliced names like
> /dev/wd0s1a rather than the /dev/wd0a I'd expect since there is only
> one slice on the whole disk. My zip drive uses /dev/da0a after I did
> a newfs on it, though.
>
> WL> FreeBSD lets you do this as well. Are you sure that Linux doesn't
> WL> require fdisk disks? Linux/i386 doesn't have another form of disk
>
> Linux requires it to run, but doesn't hang forever if it doesn't
> exist. FreeBSD is the only system I've encountered so far that will
> lock up (ie, does not respond to any keyboard requests or terminate
> its probe) when scanning a disk without an FDISK table. I needed to
> use freedos to add one to this particular drive.
What's there to scan? The MBR always lives on the first sector of the
disk. If it hung it was the BIOS that hung because it had nothing else
to do.
Do you understand how the MBR works? I didn't think so. Well here's a
course in MBR 101. We'll have a test on this material on Friday.
1. BIOS reads the first sector of the disk.
2. If the last byte of the sector != 0xaa55, stop and hang
3. If the MBR checksum doesn't match the MBR, stop and hang. (Some
BIOSes
skip this step or just complain that that a virus has been installed
and continue to boot anyway).
4. Jump to the MBR and start executing it.
5. The MBR will scan it's table of four entries and load the boot
record
from the partition that is marked active.
6. The MBR will test the last byte of the sector it just loaded for
0xaa55.
If it's 0xaa55 and if the checksum matches (some MBR's don't bother
to
check the checksum), it will jump to the boot record.
Regards, Phone: (250)387-8437
Cy Schubert Fax: (250)387-5766
Team Leader, Sun/DEC Team Internet: Cy.Schubert@osg.gov.bc.ca
Open Systems Group, ITSD, ISTA
Province of BC
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-stable" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200003231358.FAA01112>