Re: Debian + LVM + RAID1

["Damon L. Chesser" <damon@damtek.com>]

Ivan Glushkov wrote:
> Damon L. Chesser wrote:
>   
> > snip
> >     
> > > I taught I have to install the grub on the raid array, thus the grub
> > > will put a copy of itself on the first partition on both hard drives,
> > > used for the raid1, right?
> > >   
> > >       
> > Wrong  AFAIK.  You can do that IF you have a boot loader on the MBR
> > pointing to grub.
> >     
>
> Now I am confused. Isn't grub a boot loader? Why would I need another
> boot loader pointing to grub? I want to put grub on the MBR of both hard
> drives from which my raid1 array consist of.
>
> BIOS does not read software raid and knows nothing
>   
> > about software raid.
> >     
>
> Indeed, but I do not expect from the bios to read my raid array. I
> merely want it to look for boot record in the MBR of one of the two hard
> drives on which I have my raid arrays.
>
>   Software raid does not come into play until the
>   
> > kernel via initrd is loaded.  Install to the MBR of the first HD of the
> > array, then use grub to install into the MBR of the other members.
> >     
>
> What I meant with the paragraph you are referring to is exactly that:
> issuing:
>
> grub-install /dev/md0
>
> should install (as fas as I understand it) a copy of grub in each hdd
> from which the raid1 consist of (note: the partitions from both hard
> drives included in md0 are both 512 MB and starting from the beginning
> of the hard drives).
>   

Truly, I don't know if you install grub onto a raid1 if it will install 
it onto the MBR of both physical HDs.  I just always made partitions for 
the /boot, installed to one, moved the data around and made a mdX out of 
it and installed grub onto the other member.  Re-inventing the wheel?  
Probably.
> If I
>   
> > am wrong, then it is news to me, but hey, I will learn new things!  See
> > my old "howto" on Linux, grub and raid at damtek.com for the exact
> > commands.  It is not pretty, but it will work.
> >     
>
> I tried that. Thanks.
>
> Basically the problem was easily solved. I had to tag both partitions to
> be used for my /boot raid1 array as primary and bootable (stupid of me,
> I know). But there is now another problem:
>
> I see already the grub initial screen, but when I hit enter, I get the
> following:
>
> Booting 'Debian GNU/Linux, kernel 2.6.24-1-amd64'
>
> root (hd5,0)
>  Filesystem type unknown, partition type 0x7
> kernel //vmlinuz-2.6.24-1-amd64 root=/dev/mapper/vg00-root ro linux26 quiet
>
> Error 17: Cannot mount selected partition
>
> Press any key to continue...
>
> I suppose grub does not know anything about LVM and the partitions on
> that. If I am right, I have to rebuild initrd, right? But how do I tell
> it to enable the lvm?
>   

You have me there, it should have done it automagicaly when it 
installed.  Use rescue mode, but I am not sure what command you should 
use to re-generate it.  Perhaps chroot to your /, then try to run mkinitrd.

do you have a line in grub like this?

title        Debian GNU/Linux, kernel 2.6.25-1-amd64
root        (hd0,5)
kernel        /boot/vmlinuz-2.6.25-1-amd64 root=/dev/hda6 ro quiet
------->>>>>>> initrd        /boot/initrd.img-2.6.25-1-amd64 
<<<<<<<<<<<-------

If not, that would seem to mean you don't have an intrd.


--
Damon L. Chesser
damon@damtek.com
http://www.linkedin.com/in/dchesser