Re: more problems migrating to RAID1
- From: Les Mikesell <lesmikesell@xxxxxxxxx>
- Date: Sun, 26 Mar 2006 13:28:41 -0600
On Sun, 2006-03-26 at 12:56, Jack Howarth wrote:
As I mentioned before, I have succesfully created matching md partitions
on a second hard drive (hde) and populated them using tar with the contents
of the first (hda) drive.
However I am having problems booting off the md partitions using the grub
booter installed on the hda partition using the approach commonly given
of adding two entries in the front of grub.conf to boot to /dev/md2
which is the new root partition on hde.
I am wondering if I would be better off attempting to boot from the
linux rescue disk and, while chrooted in /mnt/sysimage for the hde
drives md partitions, reinstall the current kernel rpm. It seems to me
that in such a state, rpm should think the root partition is a md
partition and properly configure the created initrd.img for booting off
of it. The question I have is what does the linux rescue cd do if it
finds two different drives if linux installations on the machine? The
hde drive doesn't have a grub setup on it yet so I am concerned that
if both drive are available, the linux rescue cd will mount the partitions
on the hda one and not the hde one unless I detach the hda drive.
I am also still a bit confused about what grub does if it is installed
on the first drive (hda) which still has normal partitions but has a grub.conf
in the /boot partition on that drive that references md partitions for the
root partition (root=/dev/md2). I assume grub will try to get /dev/md2 from
the hda drive first and might generate and error before ever trying the hde
drive. I have seen at least one reference of converting the partitions on
the first drive to Raid AutoDetect even though the contents of the fstab
on its partitions still reference normal partitions. My question is whether
grub can load linux using normal partitions even if the partitions are set
to fd (Raid Autodetect). That is does the use of the fd ID for partitions
prevent those partitions from being used as normal partitions as well as
md partitions. I suspect not but am unsure.
Grub itself doesn't know anything about raid. It happens to work
with RAID1 because it can use the underlying /boot partition
on either mirror. So, the steps up to loading the kernel
are working with normal partitions (and it doesn't care about
the FD partition type), and the grub.conf entry root (hd0,0)
refers to the partitions as used by the grub loader. After
oading the kernel, it will autodetect the raid partitions that
are marked with the FD type, so you can have 'root=/dev/md2'
in the kernel line in grub.conf. That is just passed to the
kernel and grub doesn't have to understand it. You should
fix fstab to match the entry that the kernel line uses.
ps I assume in the worse scenario I can detach the hda drive, boot from
the linux rescue cd and setup grub on the hde drive to boot the md
partitions there. However I am unclear how I would ever be able to
reattach the first drive (hda) to use it for the missing spares since
it has grub setup on it.
You could, at this point swap the RAID drive into the hda position,
and install grub in rescue mode, but you shouldn't have to do
it that way. If you do, be sure the fstab entries match what
the install/rescue boot will see.
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- From: Jack Howarth
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