[CentOS] Replacing failed software RAID drive

Hugh E Cruickshank hugh at forsoft.com
Wed Oct 10 21:46:55 UTC 2007

From: Les Mikesell
> Hugh E Cruickshank wrote:
> > From: Les Mikesell Sent: October 7, 2007 18:53
> >
> >> Then reinstall grub on the drive.
> >
> > Now I have some questions:
> >
> > 1. Since the /boot partition was mirrored and will be restored on the
> >    new sda drive I do not really want to do a full grub install. From
> >    what I have read that will overwrite existing /boot/grub/grub.conf
> >    file. So I just want to write the MBR on the drive. How to I do
> >    that (the docs I have found were rather unclear on that aspect)?
> >
> > 2. Can a install grub on the replaced boot drive with the system still
> >    running?
> Yes, after the /boot partition re-sync has completed, execute grub and:
> root (hd0,0)
> setup (hd0)
> quit
> If you aren't able to keep the system running while doing the swap, you
> can also do this from the rescue mode boot, but you should have the
> contents on the /boot partition first.

Sorry to be obtuse here but I just want to make very sure of what I am
doing before I do it. Will the "setup" command only write the MBR?

>From my reading the GNU GRUB manual I got the distinct impression that
the "setup" command will also write/rewrite the /boot partition (which
I would like to avoid). The documentation for the setup command states:

    Set up the installation of GRUB automatically. This command uses
    the more flexible command install (see Section 13.3.18 [install],
    page 44) in the backend and installs Chapter 13: The list of
    available commands 49 GRUB into the device install device. If
    image device is specified, then find the GRUB images (see Chapter
    10 [Images], page 29) in the device image device, otherwise use the
    current root device, which can be set by the command root. If
    install device is a hard disk, then embed a Stage 1.5 in the disk
    if possible.

    The option ‘--prefix’ specifies the directory under which GRUB
    images are put. If it is not specified, GRUB automatically
    searches them in ‘/boot/grub’ and ‘/grub’.

    The options ‘--force-lba’ and ‘--stage2’ are just passed to install
    if specified. See Section 13.3.18 [install], page 44, for more

The second paragraph tends to imply that /boot/grub will be written
to by default and I do not think that this is what I want to happen.

Thanks again for everyone's input (especially Les). It is greatly

Regards, Hugh

Hugh E Cruickshank, Forward Software, www.forward-software.com

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