single SATA disk and yet identified as 'ad4'

Erik Trulsson ertr1013 at
Mon May 11 14:38:03 UTC 2009

On Mon, May 11, 2009 at 04:30:23PM +0200, Jonathan McKeown wrote:
> On Monday 11 May 2009 21:38:50 Saifi Khan wrote:
> > Hi all:
> >
> > The system has just one SATA disk and yet bootloader process
> > identified it as 'ad4'. Ideally, it should be ad1.
> [snip]
> > How does the labelling logic work ?
> FreeBSD reserves numbers for devices that aren't currently connected, so that 
> if you connect them later your existing devices don't need to be renumbered.

It does this if you have 'options  ATA_STATIC_ID' in your kernel config
(which is the default.) Otherwise all PATA/SATA disks installed will
numbered from ad0 upwards without any gaps.  The drawback of that is that
without the static numbering the disk devices can (and often will) be
renumbered if you add or remove a disk, which often is not desirable.

> Your BIOS is reporting two IDE interfaces, each of which could have a master 
> and slave disk drive, so ad0-3 are reserved for those four drives, meaning 
> SATA starts at ad4.
> Some BIOSes let you change this.
> Jonathan

<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at

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