FreeBSD slices and the Boot Manager

Conny Andersson ataraxi at
Sat Jul 27 17:47:28 UTC 2013


I have a workstation with two factory installed hard disks. The first disk, 
ada0, is occupied by a Windows 7 Pro OS (mainly kept for the three year 
warranty of the workstation as Dell techs mostly speak the Microsoft 

Instead I have configured the BIOS to boot from the MBR on the second disk 
as I most of the time (99%) use FreeBSD. The MBR on ada1 was installed with 
sysinstall's option "Install the FreeBSD Boot Manager", when I installed 
the FreeBSD 8.3-RELEASE.

(The latest BIOS version 2.4.0 for Dell T1500 does not support 

The second disk ada1, now has three FreeBSD slices:

1) ada1s1 with FreeBSD 8.1-RELEASE

2) ada1s2 with FreeBSD 8.2-RELEASE

3) ada1s3 with FreeBSD 8.3-RELEASE

I want to install the new FreeBSD 8.4-RELEASE on ada1s1 by overwriting the 
now existing two first slices. This means that ada1s3, must become ada1s2 
instead. Is this possible to do?

A very important question is if sysinstall's option "Install the FreeBSD 
Boot Manager" detects that I have a FreeBSD 8.3 and detect it as slice 2 on 
disk 1? So it becomes a boot option when I am rebooting? (Maybe the slice 
may come up as ad6s2, because AHCI in FreeBSD 8.4 isn't enabled at the time 
of the install.)

If the answer to these questions is yes, then the next two questions arise.

Can I mount ada1s2a (FreeBSD 8.3) from the newly installed FreeBSD 8.4 and 
edit my FreeBSD's 8.3-R /etc/fstab according to the new disk layout, and 
occasionally run FreeBSD 8.3 without problems? Or do I have to do more to 
get it to work?

The idea behind this kind of 'reverse' disk layout of mine is to have 
FreeBSD 8.4 as my new default OS. And have FreeBSD 8.3 untouched for 
configuring FreeBSD 8.4 and booting into it when ever needed. If I can do 
this as described above, I will have plenty of space on the disk for the 
future and a new FreeBSD release.

Thanks for your interest in my questions,

Conny Andersson

   Conny Andersson
<ataraxi at>

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