Need help switching between two FreeBSD boot drives

Darren David darren at
Thu Jan 5 20:18:11 PST 2006

hi all-

i've got one i've been tearing my hair out over here, and even after 
finding some information out there, i'm still totally lost. this may 
take a while to explain, so please bear with me.

I've got 2 80GB SATA drives in my FreeBSD machine, which are mapped as 
/dev/ad4 and /dev/ad6. I've got 5_STABLE installed on 1 drive, and my 
plan is to get a working install of 6_STABLE on the other drive, so i 
can take my time to work out the kinks with the upgrade on the 2nd drive 
(it hasn't been straighforward) and be able to switch back to my working 
5_STABLE machine as needed. That's the plan, anyway.

So I followed the general instructions here:

to clone drive 1 over to drive 2. very cool, no problems, i can pick 
either drive in the bootloader and boot up there. so all is well and 
good until i boot into drive 2 and start the upgrade process. I realize 
the /dev/ad4 and /dev/ad6 are not exactly fixed. It seems almost 
arbitrary which drive ends up mapped as /dev/ad6 and /dev/ad4, and this 
caused me to nearly munge all of the data on the working 5_STABLE 
install before i caught myself. If i boot into drive 1 at boot time, 
everything ends up being mounted at /dev/ad6. If i mount into drive 2 at 
boot time, the same thing happens. Mind you, i /did/ check /etc/fstab to 
ensure that all was well, but i ended up with a weird situation where, 
say, / would be /dev/ad4s1a and all of the other mountpoints were at 
/dev/ad6*. ugh. confusing!

I found this page, which explains the problem /somewhat/:

but to be completely honest, the concept didn't stick. What i need help 
with, since these drives are exactly the same size and make, is how i 
can do the following:

1) determine the relationship between Drive 1/Drive 2 and ad4/ad6
2) determine exactly which physical drive i am working on at any given 
time, since the /dev node mappings seem to be malleable
3) enable an environment where i can safely and surely boot into either 
drive and know for a fact that the right partitions are mounted ( all of 
the data on all of the partitions aside from / is mirrored, so it's 
practically impossible to tell which drive is which )
4) (bonus points) My bootloader shows the following on boot:

   F1: FreeBSD
   F2: FreeBSD
   F5: Drive 1

a) I've only got 1 FreeBSD install on this drive, so what is F2? It just 
beeps at me when i try it
b) I assume that "F5: Drive 1" means that the drive i'm staring at the 
options for is Drive 2, adn that selecting F5 will toggle to Drive 1? 
Just clarifying!

i hope this is an easy one to solve. i look forward to any and all help!

thanks in advance,
darren david

More information about the freebsd-questions mailing list