CentOS - Aug 2007 - how to find out which is the system disk by bios?

hi,
how can i know which is the system disk by bios? i've pc with 2 sata
disk connected to the on board sata controller and 2 other connected to
a pci card sata controller. bios see all disk as well as linux, but in
linux kernel sda and sdb is the pci card's 2 disks and the on board
controllers are sdc and sdd. my problem is centos install the system by
default to sda and intall grub in the system disk's mbr (ie. sda's mbr).
which is right most of the time, but in my case the system is not boot
after the install since grub (and the os) it's not on the system disk
where the bios try to find it. ok after i recognize it i can choose sdc
during install and install the whole system there, but the worse thing
is that i'd like to do it from a kickstart file _automaticaly_. so i
have to somehow discover which disk will be choosen by the bios as
system disk? or which disk is connected to the on board controller and
which is the pci extension card? how can i find out this information
(eg. by a shell script in kickstart %pre section)? and this scripts
should have to work for all kind of motherboard and sata card too:-)
thanks.

-- 
  Levente                               "Si vis pacem para bellum!"

> -----Original Message-----
> From: centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] On Behalf Of Farkas Levente
> Sent: Monday, August 06, 2007 11:14 AM
> To: CentOS mailing list
> Subject: [CentOS] how to find out which is the system disk by bios?
> 
> hi,
> how can i know which is the system disk by bios? i've pc with 2 sata
> disk connected to the on board sata controller and 2 other 
> connected to
> a pci card sata controller. bios see all disk as well as linux, but in
> linux kernel sda and sdb is the pci card's 2 disks and the on board
> controllers are sdc and sdd. my problem is centos install the 
> system by
> default to sda and intall grub in the system disk's mbr (ie. 
> sda's mbr).
> which is right most of the time, but in my case the system is not boot
> after the install since grub (and the os) it's not on the system disk
> where the bios try to find it. ok after i recognize it i can 
> choose sdc
> during install and install the whole system there, but the worse thing
> is that i'd like to do it from a kickstart file _automaticaly_. so i
> have to somehow discover which disk will be choosen by the bios as
> system disk? or which disk is connected to the on board controller and
> which is the pci extension card? how can i find out this information
> (eg. by a shell script in kickstart %pre section)? and this scripts
> should have to work for all kind of motherboard and sata card too:-)
> thanks.
This is a common problem and there is no good way for CentOS to know
which controller (and thus which disk) is the onboard controller and
thus which should be loaded first.

In this scenario YOU need to know which disk is the onboard one(s) and
select those for install.

One way around this in a kickstart is, IF the SATA controllers use a
different driver you can specify which storage driver to load in the
kickstart. I forget the exact directive, but you should find it in the
RHEL 5 kickstart docs online.

That way only the drives off that controller will be active during the
install.

-Ross

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