Re: Question about LVM or RAID on /boot

[Kun Huang]

Thanks Andrey. It's helpful : )

On Wed, Oct 16, 2013 at 10:53 AM, Andrey Borzenkov <address@hidden> wrote:

В Wed, 16 Oct 2013 09:13:05 +0800
Kun Huang <address@hidden> пишет:

> Sorry, why does that limitation stay in BIOS stage? In whole grub progress,
> we have no chance to scan all disks?
>

As long as grub is using BIOS to access them - no. It is possible to
use "native" grub disk drivers which bypasses BIOS and directly accesses
hard disk controller. On BIOS platforms that would be AHCI.

> On Tuesday, October 15, 2013, Chris Murphy wrote:
>
> >

> > On Oct 14, 2013, at 10:22 PM, Kun Huang <address@hidden<_javascript_:_e({}, 'cvml', 'address@hidden');>>

> > wrote:
> >
> > Hi all
> >
> > When searching why we couldn't use LVM or RAID on /boot, the most of
> > answers are "that couldn't be support". But I would like get to know more
> > details. In grub.conf file, we could use (hd0,0) to specify "root=". In
> > another words, grub in stage2 actually could find data in all of disks. Is
> > this right? If grub could find all partitions of all disks, what other
> > reasons stop we find out information of LVM or RAID about and in disks?
> >
> >
> > Works fine with GRUB2 for the past ~2 years at least. Probably longer.
> >
> > The limitation is BIOS seeing all of the disks, not a GRUB limitation. I
> > think there's work that needs to be done to update the GRUB LVM code when
> > it comes to LVM integrated raid levels 10, 5, and 6; and also thin
> > provisioning. Except for raid0, 1, 10, I think the rest is a bit esoteric
> > for /boot, and is probably more trouble than it's worth if there are device
> > failures.
> >
> > I don't actually know off hand if GRUB2's md raid code can rebuild data
> > chunks from parity on the fly, e.g. if there's a 1 disk failure of a raid5
> > array. If not, yeah, all the more reason I'd keep /boot simple.
> >
> >
> > Chris Murphy
> >