Date: Wed, 22 Aug 2007 14:18:46 -0400 From: Lowell Gilbert <freebsd-questions-local@be-well.ilk.org> To: Christopher Key <cjk32@cam.ac.uk> Cc: freebsd-questions@freebsd.org Subject: Re: FreeBSD MBRs Message-ID: <44k5rno2k9.fsf@be-well.ilk.org> In-Reply-To: <46CC1DB7.7040506@cam.ac.uk> (Christopher Key's message of "Wed\, 22 Aug 2007 12\:27\:51 %2B0100") References: <46CC1DB7.7040506@cam.ac.uk>
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Christopher Key <cjk32@cam.ac.uk> writes: > I've a machine with 3 SATA drives. The first (ad8) with a standard > FreeBSD install in a single slice with /boot/boot0 MBR. The remaining > two drives (ad10, ad12) are in a RAID1 mirror with 3 slices, and used > for storing data. They have the /boot/mbr MBR. > > After booting off various USB flash drives to try and update the BIOS on > my machine, it got into a state where during startup, it would display > 'Missing operating system' and hang. What seems to have been happening > is that it was trying to boot from one of my data store drives, despite > the boot order of the disks set in the BIOS. > > The only solution that I found was to start booting from a USB flash > drive with a boot0 MBR, and to hit F5 to change to booting from my first > drive After this, the machine then reboots quite happily until I hit F5 > again, in which case I get the same 'Missing operating behavior'. This > persists even while power cycling the machine. > > I had imagined the boot process to be entirely stateless, certainly > across power cycles. The BIOS executes the MBR on the first drive in > its boot boot. The boot0 MBR then allowed you to either execute the > boot sector from any of the slices on the current drive, or to execute > the MBR from the next drive in the list. > > However, this clearly isn't what's happening. Is it boot0 remembering > my F5 key stroke, or is it more likely that the BIOS is remembering > something? Does anyone have any recommendations to avoid this in the > future? Is putting boot0 on all three drives a good idea perhaps? The boot process isn't completely stateless at the best of times; it uses the partition (as in "slice") table to tell it what to boot by default. I think that explains the behaviour when you boot from the flash drive, but not when you try to boot from the SATA disk. It won't hurt, and might help, to put the FreeBSD boot manager on more of the disks. You could also try other boot managers; at the expense of having a boot manager that doesn't fit completely into the MBR, you could get something more user-friendly. Good luck. -- [Greetings to Cambridge; I spent a term in the city as a teenager (fifth form), and I loved the place.]
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