Date: Mon, 11 Nov 96 14:52:47 PST From: BRETT_GLASS@infoworld.com To: Harlan Stenn <Harlan.Stenn@pfcs.com>, rschof@mccomm.nl, michaelv@MindBender.serv.net Cc: freebsd-hardware@freebsd.org Subject: Re: After changing to an AHA2940 I can't boot the kernel. Message-ID: <9610118477.AA847750238@ccgate.infoworld.com>
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Most likely problem: the sector mapping on one controller is different from that on the other. The BIOS always tries to boot from what it sees as the first sector on the disk -- the Master Boot Record (or MBR). That's cylinder 0, head 0, sector 0. But SCSI disks don't address storage in terms of those physical parameters; they use block numbers. So SCSI controllers for the PC platform map those parameters to a block number. The mapping doesn't necessarily start at the first block on the disk, though. In fact, many controllers store private information in a few reserved blocks at the beginning of the disk. If you switch controllers, the number of reserved blocks might be different, or their contents might look like gibberish to the new controller. The only answer: back up, change controllers, repartition, make new file systems, restore. Usually, the controller writes its private information (if any) when you rewrite the MBR -- that is, as you partition. --Brett
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