[CentOS] Make Raid1 2nd disk bootable?

[David G. Miller]

Les Mikesell <lesmikesell at gmail.com> wrote:

> David G. Miller wrote:
>> > 
>>     
>>> >> Grub isn't so much the issue here as the difference in the rescue mode 
>>> >> boot.  I'm used to being able to boot the CD, chroot into the existing 
>>> >> system and have pretty much normal access regardless of what was 
>>> >> broken. Now that the system /dev directory is basically empty, things 
>>> >> don't work   when you have to mount the partitions manually.  Is there 
>>> >> a step to set up devices so the chroot will work?
>>>       
>> > 
>> > I haven't tried this but were you looking at /dev *after* you did the 
>> > chroot?  It sort of makes sense to me that the running kernel would only 
>> > populate it's /dev, not the chrooted /dev.  Rescue mounts at least the 
>> > root partition under /mnt/sys (or something like that).  Before you 
>> > chroot, you should probably also mount any other partitions you want 
>> > under /mnt/sys and then chroot.
>>     
>
> It makes sense for the boot code, but not for me afterwards...  The real 
> problem is that the rescue mode startup doesn't mount RAID1 partitions 
> at all (this seems like a bug).  The startup code might populate the 
> chroot'ed /dev if it had done the mount - I just haven't found how to do 
> it myself after doing the mount by hand.  Thus there's no /dev/sda or 
> /dev/sdb as you'd expect when you want to install grub.
Let me try explaining this a different way.  After you let the rescue 
software mount the partition, *don't* chroot. 

It's been a long time since I had to mess with booting in rescue mode 
but lets assume your old root partition gets mounted under /mnt/sysimage 
and you told the rescue software to go ahead and mount it.  If your 
/boot is a separate partition, you'll need to mount it manually.  
Assuming you keep everything where it belongs, mount it under 
/mnt/sysimage/boot.  Then run grub by doing:

/mnt/sysimage/sbin/grub --config-file=/mnt/sysimage/boot/grub/grub.conf

This way grub "sees" /dev for the running system but uses your real grub 
config file.  You may want to confirm that grub.conf has what you want 
in it.

Cheers,
Dave

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