Fixing a MBR (and more) that ??? trashed

[Alex Zbyslaw]

Gayn Winters wrote:

>>-----Original Message-----
>>From: Alex Zbyslaw [mailto:xfb52 at dial.pipex.com] 
>>Sent: Wednesday, September 14, 2005 1:59 AM
>>To: gayn.winters at bristolsystems.com
>>Cc: freebsd-questions at freebsd.org
>>Subject: Re: Fixing a MBR (and more) that ??? trashed
>>
>>Gayn Winters wrote:
>>
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>>>>Alex Zbyslaw [mailto:xfb52 at dial.pipex.com] 
>>>>   
>>>>Why do you think it's not safe to add hard drives?
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>>>>
>>>It doesn't seem "safe" if Windows blows away the multiboot MBR that
>>>FreeBSD so carefully made!  Windows overwriting the MBR 
>>>      
>>>
>>seems to be the reason people recommend loading Windows before loading
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>
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>>FreeBSD, which I do.  I just never realized that this problem would
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>come back 
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>>to bite me when I added another disk drive.
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>>> 
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>>I know of know reason why it should.  I've added disks half a dozen 
>>times without blowing away any MBRs.  Even the Windows blowing away
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>the 
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>>MBR is an annoyance, not a disaster since it is easy to rewrite.  
>>Whatever pickle you find yourself in seems to have to do with 
>>more than just adding a disk or Windows killing your MBR.
>>
>>--Alex
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>
>I certainly am willing to admit that I'm doing something stupid!
>The motherboard and its BIOS are also known to be strange.
>
>One thing to note is that if I reconfigure (fresh FBSD install), add
>hardware, and then boot first into FBSD, all is well EXCEPT the boot
>loader, whose prompt is:
>	F1 ???
>	F2 FreeBSD
>	F5 Drive 1
>
>	Default: F2
>
>If I select F2, then I get FreeBSD.  If I select F5 I get Windows!  I.e.
>F5 gives me the same slice as does F1!!!  (Drive1 is the extra IDE
>drive.)  I can't blame Windows for this, since it never got booted.
>Also, if FBSD gets booted first, Windows doesn't (further) corrupt the
>MBR.  Incidentally, rewriting the MBR with
>	boot0cfg -B -o packet /dev/ad1
>does not change anything.  The F5 option is still there, and it still
>brings up the Windows that is on slice1.  If I add a third IDE drive,
>the situation also remains the same.  In particular, I don't get an F9
>option.
>
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I know too little about your setup.  Are you sure ad1 is your second 
disk?  (There's nothing to stop you booting from any disk whatsoever if 
you BIOS allows, and many do).  When you boot off F2, what does say df show?

If you had a FreeBSD MBR on the second disk, then you *ought* to get 
another F1, F2 etc menu.  If you have a third disk, then the second disk 
would also have an F5 option e.g.

    DISK1             DISK2              DISK3
    F5->DISK2       F5->DISK3       F5->DISK1

There's never anything higher than F5 since there can never be more than 
4 slices on a disk (F1-F4), plus F5 for the next disk (if any).

--Alex