i have two scsi-disks in my system and would like to use the second disk as backup system. i have already cloned the files from the first disk and would like to make it bootable now.

the problem is, that i have to change the boot device in the scsi-bios of my adaptec 2940uwpro so that the system knows that i want to boot from my backup-disk, not from my normal disk. but as soon as i change the boot-id to the backup-disk, that disk becomes sda and the old sda gets sdb. this seems to confuse lilo and grub.

with lilo i tried to get around this by using the disk= and bios= options, but it doesn't work, regardless if i declare sdb as 0x80 or sda, i only get a LI.

then i tried grub and installed it to sdb, but if i change the drive-id's and try to boot it i only get a screen full of 'GRUB's.

i don't want to boot from a floppy just to fix this, because that would mean i can't make a backup from the running system. so i'm looking for a sollution where i can (re)install grub or lilo on the second disk on-the-fly if necessary and be still able to boot from it after sda<->sdb changed.

any ideas how this could be done?

i found a way to install grub on the disk in native mode (even though i'm not so sure why it didn't work in the first place or what i did differently this time). it seems that grub is flexible enough not to care too much about the device-names during installation.

so just a short question that remains: does grub work as long as the needed files are in /boot/grub or is it essential that the files don't change their position? so if i'd delete them and copy them to /boot/grub again, will grub still load?

Gee, here's how your PC boots.

BIOS > boot sector of HD > boot loader > OS (kernel)

Now you can start thinking...

you can also map the drives around with lilo/grub. read the docs for info about that.

sl mritch

maybe you misunderstood my question: the boot-sector is, as the name suggests, a sector. but how does grub find it's own files, e.g. the stage files or the kernels? by reading the files, i.e. knowing the file system structure or by remembering absolute sectors (as lilo did, if i understood it correctly)? because if the addressing is done by sectors i can't move the stage files, even if they end up in the same folder after that.

As I understand it there are two options for installing grub
1. stage1 /stage2

stage1 is installed on the boot sector, so the BIOS knows where to find it.. The location of stage2 is patched in the stage1 before it gets placed on the boot sector. stage2 understands the filesystem, so it knows where to find menu.lst.

Once installed, you can not move stage2.

2 stage1 / stage1.5 / stage2
stage1 is installed on the boot sector, so the BIOS knows where to find it.. The location of stage1.5 is patched in the stage1 before it gets placed on the boot sector. stage1.5 knows enough of the file system to be able to locate and load stage2 wherever that is.

I don't quite understand the advantage of the second scheme, because you're still stuck with a file (stage1.5) that cannot be moved