Bug#685782: linux-image-3.2.0-3-686-pae: Upgrading from 3.2.0-2 to 3.2.0-3 no longer boots using 3ware 9500S RAID card.

[Ben Hutchings]

On Fri, 2012-08-24 at 20:08 -0400, Jon Daley wrote:
> On Fri, 24 Aug 2012, Ben Hutchings wrote:
> >> It seems like the 3w-9xxx driver no longer supports the 9500S series?
> >
> > A bug in a driver, should it exist, won't retroactively stop GRUB from
> > having loaded the kernel in the first place...
>  	Is that really true?  If a RAID controller driver doesn't load 
> properly, then the kernel can't be loaded at all, right?

Wrong.  Drivers don't load the kernel, the bootloader loads the kernel
and the initramfs, and then the kernel loads the drivers.

Anticipating the following questions:

"But how does GRUB load the kernel without using a driver?"

It kind of does.  It uses BIOS calls, and the RAID controller has an
'option ROM' that hooks into the BIOS and implements a boot-time driver.

"Why does the kernel need another driver, then?"

Because the boot-time driver is not very advanced or efficient.

"So how does the kernel load drivers from disk without a driver for the
disk?"

They're included in the initramfs which is loaded by the bootloader.

>  	It seems odd to me that it would be a grub bug, since I can make 
> it work by only changing the version of the kernel.  But, you know more 
> about this than I do, for sure.

No, I don't understand this either.  But since things are going wrong
even before the kernel is loaded, I think this needs the expertise of
the GRUB maintainers.

Ben.

-- 
Ben Hutchings
Experience is what causes a person to make new mistakes instead of old ones.
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