Date: Wed, 22 Aug 2007 12:27:51 +0100 From: Christopher Key <cjk32@cam.ac.uk> To: freebsd-questions@freebsd.org Subject: FreeBSD MBRs Message-ID: <46CC1DB7.7040506@cam.ac.uk>
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Hello, 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? Regards, Chris
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