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Re: Bug report added



mcforum bellsouth net wrote:
> 
> You have it all worked out.  The system now makes whichever drive has the root 
> filesystem /dev/sda.  When you boot from the rescue disk the SATA bus on your system 
> takes precedence over the IDE bus on your motherboard since neither harddrive has 
> the root filesystem.  When you boot F7-64 its root defines which drive shows as /dev/sda.
> 
This is NOT correct. The first disk drive that is handled as a SCSI
drive becomes /dev/sda. There is nothing preventing you from having
the root file system on /dev/sdb, /dev/sdc, etc. Where you run into
problems is when you tell the BIOS to boot from the SATA drive, or
the PATA drive. Depending on the BIOS, it this can change witch
controller is found first by the kernel. If the PATA and SATA
interfaces are not using the same driver, or if you add a "real"
SCSI controller to the mix, then the driver loaded by the initrd
controls what the first SCSI controller is, and the first hard drive
on that controller becomes /dev/sda.

To make things more interesting, if the BIOS does not change the
order of the controllers, then the BIOS numbering that Grub changes
depending on what drive you boot from, but the kernel mapping of the
drives does not. This can lead to a case where the BIOS boots off
the SATA drive, but the PATA drive is /dev/sda. In this case, the
SATA drive is hd0 as far as Grub is concerned, but the PATA drive is
/dev/sda. But if you remove the PATA drive, then the SATA drive
becomes /dev/sda.

To have more fun, I have a USB drive with F7 on it. If I tell the
BIOS to boot from that drive, then that drive is hd0 as far as Grub
is concerned. If I boot Linux from that drive, then it becomes
/dev/sda because the usb_storage module is loaded by the initrd, but
the IDE drivers are not. On the other hand, if I build an initrd
that loads the IDE driver first, and then the usb_storage module,
then it will be /dev/sdb, or /dev/sdc, depending on what system I
have it plugged into. As long as I use labels, it will still work.

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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