[CentOS] install detecting disk as sdb not sda

[Ross Walker]

On Feb 3, 2012, at 5:02 PM, wwp <subscript at free.fr> wrote:

> Hello Ross,
> 
> 
> On Fri, 3 Feb 2012 16:01:53 -0500 Ross Walker <rswwalker at gmail.com> wrote:
> 
>> On Feb 3, 2012, at 1:34 PM, wwp <subscript at free.fr> wrote:
>> 
>>> Hello Jerry,
>>> 
>>> 
>>> On Fri, 03 Feb 2012 12:24:14 -0500 Jerry Geis <geisj at pagestation.com> wrote:
>>> 
>>>> I am trying to install 6.2 on a machine.
>>>> I am using PXE as I have done so a number of times.
>>>> 
>>>> My hard disk is being detected as sdb and not sda.
>>>> My kickstart config is wanting it at sda.
>>>> 
>>>> There are no other disks in the unit. It has and SD slot and an esata
>>>> although BIOS does not appear to have a disable for either of those devices.
>>>> 
>>>> Is there anyway to "force" the disk to sda ?
>>>> or find out what its detecting at sda and disable that from the PXE boot 
>>>> line?
>>>> 
>>>> Doing " dmesg | grep sda" does say SCSI removable disk.
>>>> 
>>>> So how can I tell linux to NOT include that when installing?
>>> 
>>> I noticed that behaviour with my CentOS6 (installed and kept up-to-date
>>> using yum). This happened since kernel kernel-2.6.32-220.el6.x86_64 and
>>> furthers updates. Was working as expected (my laptop's hdd mounted as
>>> sda) with previous kernels, up to kernel-2.6.32-131.21.1.el6.x86_64.
>>> 
>>> I wonder if that behaviour, and the *change* of behaviour is an issue
>>> that should be reported, and how to handle it on installed systems!
>>> For now, I'm either booting w/ no USB disk plugged, or booting
>>> a 2.6.32-131 kernel.
>> 
>> You can try disabling USB disk support in the bios.
> 
> Right, but I can't make such settings permanent, as I need to boot from
> a USB disk from time to time, thus, entering BIOS and changing settings
> costs more than unplugging stuff :-).
> 
> An aspect of the problem w/ that behaviour change introduced w/ recent
> kernel updates, is that some mount mapping tables (fstab for instance)
> are broken if they rely on mount order (sda, hda, etc.) instead of
> device ID or label.

I remember faintly there was abway to specify module order in C5 modprobe and regenerate the initrd to make it persistent, but I don't think C6 uses modprobe. Maybe there is an initrd option under /etc/sysconfig.

Once that's done you can re-enable USB disk support in the BIOS.

-Ross