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From: Jonathan McKeown <j.mckeown@ru.ac.za>
Organization: Rhodes University
To: freebsd-questions@freebsd.org
Date: Mon, 11 May 2009 16:30:23 +0200
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Subject: Re: single SATA disk and yet identified as 'ad4'
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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.

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