Re: How make boot loader or kernel on USB stick use another device as root FS, e.g. a BIOS-unsupported PCIe NVME SSD?

On 2018-02-01, tinkr@openmailbox.org <tinkr@openmailbox.org> wrote:
> Hi, so, this question sprung from the previous email however it's a big
> one and so deserves to be addressed separately:
>
> If a machine's BIOS does not support booting from a particular boot
> medium where OpenBSD is installed, e.g. my BIOS does maybe not
> supporting booting from PCIe NVME SSD:s, but it does support booting
> from USB memory sticks.
>
> For such situations, how can I create an OpenBSD USB stick boot disk,
> that continues the OpenBSD boot process for me but from the PCIe NVME
> SSD-stored crypto softraid?
>
> This could be done either by
>
> * The OpenBSD kernel being stored on the USB stick, loading from it,
> and then using the PCIe NVME SSD as both root disk, swap disk, and
> dump disk, or,

I think this should be possible with a custom kernel to set the
devices. Updates will be annoying and it will be tough to get KARL
to work nicely.

> * The OpenBSD boot loader which is stored on the USB memory stick,
> would load the OpenBSD kernel from the PCIe NVME SSD.

The boot loader uses BIOS IO functions, if those can't talk to the
NVME it's not going to work.

> This should be a fundamental and trivial usecase to OpenBSD, however,
> last time I tried (then with adding a "boot" command to boot.conf per
> http://man.openbsd.org/boot.conf ), I think it not worked out of the
> box.

It might not be very appealing but afaict the only trivial way to do
this is to place root on the USB stick or some other device, and other
filesystems on NVME.