grub problem after raid resynch (I PAY FOR HELP)


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Thread: grub problem after raid resynch (I PAY FOR HELP)

  1. #1
    Join Date
    Apr 2014
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    1

    grub problem after raid resynch (I PAY FOR HELP)

    So i have a server on OVH with CentOS5. One of the HDD was failing so we had to replace it.

    We did the RAID resynchronisation (RAID-1) but then the server can't boot. The error is "select proper booting device and reboot"

    We have tried a couple of things but nothing solved the problem (see here = http://www.webhostingtalk.com/showthread.php?t=1367341)

    We're currently in Rescue Mode and we are still looking for a solution. Formatting and starting over isn't an option.

    We are willing to pay if someone wants to login into our server and solve the problem for us, unless you are some untrustworth user with low posts.

  2. #2
    Join Date
    Jun 2004
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    Newcastle upon Tyne
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    2,978
    My guess is when the hdd is replaced only the filing system was transfer but not the first 512bytes sector which contains the stage I of Grub.

    You have not indicated the version of Grub but my guess is that it should be Legacy version or Grub1 since even the latest CentoOS Ver 6.5 still uses Lagacy Grub.

    The problem may be simpler than the OP thinks as the installation CD of Red Hat or Cento has a rescue mode with which the installer will find the installed Grub files and make the link. So have a go with the installation CD first. It should be in one of the options when the CD is booted and if my memory serves me right it is called "rescue" mode.

    If everything fails the problem can be resolved easily by a Grub floppy or CD. One can put Legacy Grub on a floppy or a CD and the procedure is documented in Legacy Grub manual available in the GNU/Grub web page. All one needs to do is the identify the partition that has /boot inside as Grub is always in one of its subdirectories like /boot/grub.

    Say this partition is sda0 (Legacy always count fron zero so sda0 is the 1st partition of the 1st hard disk known in Grub commands as (hd0,0)) just boot up a Grub floppy or Grub CD to a Grub prompt and type
    Code:
    root (hd0,0)
    setup (hd0)
    When the damage hdd was replaced it should be by default has all the files and subdirectories replicated. However the first sector is the MBR and has no file inside except the boot code. All copying commands of Linux (or any operating system) do not touch the boot sector for safety/security reason. The boot sector is always restored by its own boot loader by over write the existing one.T

    he above commands tell the boot-up Grub in the memory to link the stored Grub in (hd0,0) and install the link in (hd0) which is the 1st boot disk. By not supplying the partition number the link will automatically goes to the MBR. Therefore the installed Grub will used the boot code stage I from the specified /boot/grub directory and hard-code the necessary link to the MBR of hd0.

    The above problem might not appear if the damaged disk was the second boot disk in the PC connection as the boot loader is always installed in the first disk of a Raid system. Grub does not touch the second hdd of Raid1 for booting.

    Hope the above helps. Let us know if you still have a problem.

    For working with a MSDOS partition hdd (not GPT) every boot loader has two parts. Stage I must fit into the first 512 bytes which every Bios reads as a matter of routine. It is the Stage I if successfully loaded into memory that boots up the second Stage II. Your replaced hdd using normal copying command could not transfer the boot sector and the correct tool is command "dd" if the boot sector is to be copied. Using Grub1 is by far the safest way. The error you got was the Bios found the MBR of the replaced hdd empty. That is all.
    Last edited by saikee; 04-26-2014 at 04:55 PM.
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