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SubjectRe: Force a usb drive to be /dev/sda?
First, thanks a lot for the responses, especially to Stefan for the
various options. I have further questions on these options to fully
understand them.

>> Is there a reason why you can't use filesystem labels or UUIDs?
>
> Indeed. Shawn, I see these options:
>
> 1. Mount filesystems by UUID or by label.
> Doesn't work with some filesystems.

The bootloader I'm using is LILO. So I have to specify the boot device
and the root device in lilo.conf. For example, boot=/dev/sda,
root=/dev/sda1. I'm not sure how mounting filesystem by UUID or by
label can help. A little bit elaboration will be more helpful.

> 2. Refer to devices by device ID or by device path.
> Requires a minimal udev environment which gives you
> /dev/disk/by-id or /dev/disk/by-path, or something
> similar to udev. People had things like this already
> working under Linux 2.4, using programs like devlabel
> IIRC. Requires you to set up an initrd with respective
> scripts in it.
> By-path only works if you never alter the USB topology
> and PCI topology. I.e. prefer by-id.

Every USB thumb drive has a unique ID. So will I have to have a
different root filesystem image if it's install in a different usb
drive if the by-id way is adopted?

> 3. Influence the order of disk probing so that your USB
> disk is the first one. Works only if there is at most
> one disk on the USB bus and requires you to wait with
> insertion or probing of the SATA controller driver (PCI
> driver) until after the USB disk was probed by sd_mod.
>
> There may or may not be very simple ways to do this.
> Simplest would be to configure the SATA controller driver
> as module and load that module in an rc script after the
> root filesystem was mounted. That would actually be much
> simpler than option 2, so maybe you want to try this
> before 2.

I think I understand this option. Of course this requires an initrd or
initramfs, which I need to build.

> 4. Last resort: Hack sd_mod to defer any probes until after
> the first probe of an USB attached disk. Requires some
> experience in kernel driver programming.

As you said, this is the last resort, which I also try to avoid. ;-)

-Shawn.


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