Quick fix first - more added later:
If you remove the second IDE drive, and make a boot floppy, you can put
the second drive back in and boot from the floppy. (see mkbootdisk)
On Mon, 5 Feb 2001, Michael Jinks wrote:
> Wonderful, this is all becoming clear now, thanks Mikkel. More
> interspersed below.
>
>
> "Mikkel L. Ellertson" wrote:
> >
> > Ok, this tells me a lot more about what is going on. Now, does the
> > system boot off the SCSI drive, or the IDE drive?
>
> The IDE drive.
>
> > difference on how to fix this problem. From the sounds of things, you
> > are booting off the IDE drive, with /boot on the SCSI drive.
>
> Correct.
>
> > If this is
> > the case, then adding the IDE drive will mess up LILO, because the BIOS
> > number of the drives changes.
> >
> > If you have a BIOS option of booting off the SCSI drive, then you can
> > fix LILO so it will install and boot off the SCSI drive with no
> > problems. Adding the following lines to /etc/lilo.conf and running lilo
> > fill write the boot loader to the SCSI drive, and let it boot.
> >
> > boot=/dev/sda
> > disk=/dev/sda
> > bios=0x80
>
> I've revisited the lilo.conf manpage, but I'm still a bit confused
> here. From lilo.conf(5) it seems that the disk numbering from the BIOS
> can be unpredictable, is that correct?
>
Not so much unpredictable as undetectable after Linux boots. If I know
the BIOS settings as to whether you are booting from SCSI or IDE, and
how many of each drives you have, as well as how many drives the BIOS
keeps tract of, then I can tell you the numbering. But the BIOS
settings are not detectable after booting the OS because they are not
stored in standard places. Being able to select booting from a SCSI
drive, or from a CD-ROM is not a feature of all BIOSs, and a lot of
older BIOSs only know about 2 drives.
>
> > This tells lilo the BIOS mapping of the drives.
> >
> > If you are booting off the IDE drive, then the BIOS mapping with one IDE
> > drive is:
> >
> > 0x80 1st IDE drive.
> > 0x81 1st SCSI drive.
> >
> > When you add another IDE drive, it changes to:
> >
> > 0x80 1st IDE drive.
> > 0x81 2nd IDE drive.
> > 0x82 1st SCSI drive.
>
> This now makes perfect sense.
>
> Might this also explain why I was never able to boot from my SCSI drive
> in the first place? I set up lilo.conf to specify the SCSI disk as the
> boot disk, set my SCSI BIOS to boot that drive, and enabled the "Boot
> from SCSI" option on my motherboard (no onboard SCSI, I'm using an
> Adaptec PCI card). The system would wake up, successfully load the SCSI
> BIOS, report that a system image had been found on scsi0, and then sit
> there; no LILO, no LI, nothing. Different error but given that I had
> such a profound misunderstanding of the way LILO works I'm wondering if
> I might have been having LILO problems all along?
>
>
Yes. What happens is that LILO defaults to IDE drives being mapped
before SCSI drives, unless you tell it different. That is what the
disk=/dev/sda
bios=0x80
pair does. It says that the first SCSI drive will be mapped as the
first hard drive (0x80) by the BIOS at boot time. You can also add
disk=/dev/sdb
bios=0x81
if you have a second SCSI drive, because the BIOS will normaly map the
first two SCSI drives before the IDE drives. It gets more fun because
some BIOSs will only map the SCSI drives if they have SCSI id 0 and 1.
A fair number of BIOSs will only boot off SCSI drive ID 0. If your SCSI
boot drive is ID 0, you can have problems booting from SCSI.
Note: This is a limit of the PC BIOS, and not the SCSI interface. You
can get spoiled by a Sparc system - you can boot off of any device on
the SCSI chain. (Yes, you can boot off a SCSI tape...)
Mikkel
--
Do not meddle in the affairs of dragons,
for you are crunchy and taste good with ketchup.
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