Re: md extension to support booting from raid whole disks.

[Goswin von Brederlow <goswin-v-b@web.de>]

Dan Williams <dan.j.williams@intel.com> writes:

> On Fri, May 1, 2009 at 2:04 PM, Goswin von Brederlow <goswin-v-b@web.de> wrote:
>> And is horribly ugly when you have to switch hardware. And try doing
>> it with disks from different controlers? What bios supports that?
>
> This is just a simple trade-off between two options.
>
> 1/ If you want to reliably boot from multiple disks then make a native
> md-raid1 array for /boot like hpa suggests.

Which still has the same problems as the raid5. How to handle the
bootloader. Say I have a raid1 over sda/b with lvm on it. How do I
boot that? How do I get the bootloader cloned to a new spare disk when
it gets added?

It realy makes no difference if it is a raid0/1/10/4/5/6.

> 2/ If you do not want to make /boot into an md-raid1, and you still
> want to boot from raid5, then use $VENDOR's raid5 option-rom and
> mdadm's external metadata support.

There is no such thing as $VENDOR's raid5 option-rom in pretty much
all cases. And even raid0/1 roms are horribly.

> There is no third option with native md-raid5 and grub2 because as
> Gabor and hpa point out it is not reliable and will break.

And they can still be wrong.

>> What bios even supports raid5?
>
> Just look for any off-the-shelf motherboard that says it has onboard
> raid5 support and is not using a dedicated hardware raid controller.
>
> Regards,
> Dan

MfG
        Goswin