Re: Booting RHES4-U2 from mirrored disk - SOLVED

Ramer Ortega <ramer.ortega@xxxxxxxxxx> · Fri, 27 Jan 2006 20:08:39 +0300

Thanks Alfred.  Yeah, I realized, it was a chicken-and-egg situation.
As I was waiting for reply, I found this document:
Remote Conversion to Linux Software RAID 1 by Warren Togami
URL: http://togami.com/~warren/guides/remoteraidcrazies/
Step 25 of the document is about reinstalling GRUB on BOTH disks which 
is similar to what you suggested.  I followed the steps in Togami's 
document (which is an interactive session of grub) and my server can 
boot from the mirrored disk now.
Thanks once again.

Alfred Hovdestad wrote:
The problem is that you are using software raid, so there is no raid 
device /dev/md0 until the OS boots, but you can't boot because there 
is no boot device (catch-22).
We recently worked through a similar install on an HP xw9300.  We 
submitted our findings to HP, they verified them, and the last I 
hearde was that this was an "unofficial" document (I don't know if 
they ever supported the procedure, but they did verify that it worked).
It looks lke you have the raid system configured, and the OS 
installed.  All that remains is to duplicate the boot partition.  Here 
is the procedure for duplicating the boot partition:

Duplicating the Boot Partition:
1. The first step you need to accomplish is to boot into “single user” 
mode. The easiest way to accomplish this is to enter “init 1” at the 
command prompt in a terminal window. NOTE: You will need to be logged 
in as ROOT to perform these steps
2. At the prompt, type in "vi /etc/mtab". Locate the entry /dev/md0 
and replace it with /dev/sda1. Exit vi, saving your changes. Make note 
of the changes made in this and the following steps as they will need 
to be restored to their original values in the final step.
3. Next, enter "/sbin/grub-install  /dev/sda" and press ENTER, this 
will place the GRUB Boot Loader in the boot sector of  the first HDD. 
When the operation is complete it will report back that the 
installation has completed and report any errors if detected. Now, 
restore /etc/mtab to it's original contents.
4. Next, type in "vi /etc/mtab" again. Locate the entry /dev/md0 and 
replace it with /dev/sdb1. Exit vi, saving your changes.  Type in "vi 
/boot/grub/device.map" and replace the entry “/dev/sda” with 
“/dev/sdb”, exit vi, saving your changes.
5. Next, enter "/sbin/grub-install  /dev/sdb" and press ENTER, this 
will place the GRUB Boot Loader in the boot sector of  the second HDD. 
When the operation is complete it will report back that the 
installation has completed and report any errors if detected. Now, 
restore /etc/mtab to its original contents and then restore the 
content of /boot/grub/device.map to its original contents.
6. Reboot the system, the RAID1 is now completed.

     Alfred Hovdestad, RHCE
     University of Saskatchewan

Ramer Ortega wrote:
I'm trying to install RHES4-U2 in a mirrored SATA disks.  I have 2 
disks and during the installation, I defined all the partitions as 
Software RAID and eventually created RAID1 for each partition, 
including the /boot partition.
Install went smoothly but after the completion and during reboot, the 
screen simply displays "GRUB".
I booted from the install CD and entered the rescue mode to check the 
partitions and the grub.conf.  The contents of /etc/fstab rightfully 
shows that all my partitions are mapped to the corresponding /dev/md? 
devices.
My question is, is there any limitation on grub to boot from a 
mirrored /boot partition?
Is there any other area that I should be looking at?
TIA

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Re: Booting RHES4-U2 from mirrored disk - SOLVED

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