Re: Booting an old PC to SSD that the BIOS cannot see

[Narcis Garcia]

El 30/12/20 a les 19:32, Robert Furber via Support requests for the
GRand Unified Bootloader ha escrit:
> 
> On 2020-12-30 1:39 a.m., Pascal Hambourg wrote:
>> Le 30/12/2020 à 08:08, Glenn Washburn a écrit :
>>> On Tue, 29 Dec 2020 15:33:50 -0800
>>> Robert Furber via Support requests for the GRand Unified Bootloader
>>> <help-grub@gnu.org> wrote:
>> (...)
>>
>> The heavy job is done after the kernel and initramfs have been loaded
>> by GRUB, and does not use /boot.
> Obviously I need to learn more about initialization. I was under the
> mistaken impression that all the initialization was done by Grub. Can
> anyone point me towards step by step documentation that explains how a
> Linux PC is initialized? What role ramfs plays? What programs initialize
> the various h/w devices, file systems, etc.? Is it done by the Linux
> kernel?
> 
> Presumably, it is the post Grub initialization s/w that takes that takes
> time. And, it has to be accessed from the boot drive recognized by BIOS.
> If this is the case, it may be theoretically possible to split the
> initialization with step1 on the boot drive that initializes the NVMe
> SSD and step2 on the NVMe that initializes everything else.
> 
> The expedient solution appears to be to use a small, cheap SATA SSD as
> the boot drive and the NVMe SSD as the working drive, for everything
> else, a la Chris Green.

As far as I know, GNU/Linux operating systems have 2 initialization
stages after boot manager: initramfs (it's a micro OS itself, for Linux)
and Init system (such as Systemd or SystemV).

And as far as I know, BIOS only should find boot manager in a device
(such as GRUB): In BIOS mode it only needs to find sectors, and in EFI
mode it needs to understand boot manager partition.
Next the boot manager (such as GRUB) is what needs to understand any
file system useful to look for OS init/kernel.