FreeBSD MBRs

[Christopher Key]

Alex Zbyslaw wrote:
> 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
>
>
Thanks Jerry, Lowell and Alex,

That clarifies a few points.  Sorry the original post wasn't clear, I'll 
have a go at rexpressing my original questions using the above for context.

Firstly, when you hit F5, does it, a) Load the partition table from the 
next disk and update the displayed list of slices, or b) Execute the MBR 
from the next disk?  I'll assume the latter.

Secondly, does boot0 'remember' that you pressed F5, and hence do the 
same the next time you boot, even after a power cycle?  In this case, 
having done,

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

the next time, it will appear as,

Disk3: F1 -> boots FreeBSD



The behaviour that I was experiencing was as follows:

Disk1: F1 -> boots FresBSD

reboot

Disk1: F5 -> disk2
Disk2: Has /boot/mbr on it, and hence attempts to boot the active 
slice.  As there is no active slice on the disk, simply fails with the 
message 'Missing operating system'

Now, subsequent attempts to boot simply display the message 'Missing 
operating system'.  Hence, I concluded that either, a) boot0 was 
rembering the F5 keystroke, and passing me on to disk 2 automatically, 
or b) That the BIOS was rememering something and booting straight from 
disk2 despite the boot order having disk1 first.

The only was that I found to rectify this was use a boot from a USB 
device with boot0 on it:

USB: F5 -> disk1
Disk1: F1 -> boots FreeBSD

And now, subsequent reboots work fine:

Disk1: F1 -> boots FresBSD


I hope the above is a little more clear now.

Regards,

Chris