adding disk moves ad0 to ad4

Polytropon freebsd at
Wed Feb 3 17:54:18 UTC 2010

On Wed, 3 Feb 2010 10:35:48 -0700, Steve Franks <bahamasfranks at> wrote:
> Just curious, having read the handbook section talking about freebsd
> going straight to the hardware and skipping the bios for disk
> numbering, why then, if I stick a sata disk in 'sata0' on the
> motherboard, does it come up as ad0, but if I add a second disk in
> 'sata1' or 'pata0', on the next boot, I have no ad0, but ad4 and ad6?
> This seems to be the case with every mobo I've owned in the last 2
> years from a variety of mfr's.  Is there a way around this? 

Maybe this is specific to your motherboard. As far as I
experienced, using (P)ATA and SATA - or not using it -
keeps the numbering intact, e. g. ad0 - ad3 is ATA,
ad4 - ad7 is SATA, no matter where a disk is actually

It's possible that your BIOS does something strange in
representing one SATA, but no ATA disk as ad0, "the first
disk existing", as well as if an ATA disk would be present,
but no SATA disk.

I can understand that this is annoying.

> I don't
> care what it comes out as, as long as it stays put... 

There are labels or UFSIDs you can use to identify partitions
on a disk regardless of the device name they would come
out as. See "man glabel" and "man tunefs" for details.

> Since I have
> the only fbsd system at work, I tend to format alot of funky drives
> for people, and it gets anoying having to swap fstab's every time...

Labels can really help here: /etc/fstab will then contain
labels or UFSIDs instead of device names - and they don't
change when a disk is added or removed.

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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