FreeBSD MBRs

[Alex Zbyslaw]

Jerry McAllister wrote:

>You only need an MBR on disks that will be booted.  I don't know as
>it will actually hurt anything to write an MBR on non-boot, data only
>disks, but it can garbage up you menu with non-functional choices.
>  
>
What you need is an MBR on every disk which is *passed through* or 
actually booted from.  So if you have disks 1, 2 &3, if you want to boot 
from disk3 you need an MBR on disks 1 & 2 as well, even if you never 
boot from them.  If you boot from disk 1, then 2 &3 do not *need* an MBR.

>Those other disk with an MBR show up as an F5 and maybe F6, etc (
>
F5 is the *next* disk.  There is no F6, F7 etc.

If you boot from disk 3, for example, you'd go through three "menus" e.g.

Disk1: F5 -> disk2
Disk2: F5 -> disk3
Disk3: F1 -> boots FreeBSD

If those were your only 3 disks, then F5 on disk3 takes you back to disk1.

You can probably change the boot order of those disks in your BIOS to 
make disk3 be disk1, avoiding the intermediate menus. 

That's not always possible for other reasons.  For example, in the setup 
above, if disk 1 has Windows on it and that really does work best as 
disk1.  If disk 2 is on the same controller as disk 1 your BIOS might 
not allow that to be changed independently.

I know of no reason why you wouldn't want the MBR on all your disks, 
even if you don't technically need it.


Sorry, no idea if this helps with the original question, which I too had 
trouble following.

--Alex