[CentOS] CentOS 6.2 software raid 10 with LVM - Need help with degraded drive and only one MBR

Fri Mar 2 17:07:44 UTC 2012
Digimer <linux at alteeve.com>

On 03/02/2012 09:03 AM, Jonathan Vomacka wrote:
> CentOS Community,
> I have a dedicated server with 4 hard drives in a RAID 10 software 
> configuration running LVM. My OS is CentOS 6.2. Earlier today, I 
> rebooted my system and my system did not come back online. I opened a 
> ticket with my datacenter who informed me that one of my hard drives is 
> no longer recognized by the bios and has failed. I was told that an OS 
> reinstall was needed.
> I don't understand why a reinstall would be necessary when the drives 
> are in RAID 10. Apparently when the datacenter did the initial OS 
> install, they ONLY installed the MBR on one drive instead of all 4 
> leaving the other 3 drives unbootable.
> Is this a way to salvage this with a liveCD without having to reload the 
> OS? This server is a very important mail server running OpenLDAP and 
> MySQL. I figured maybe I could install the MBR using a liveCD which may 
> fix the system.
> If an OS reload is the ONLY option, is there a way to reload it without 
> touching the /var or /opt filesystems? (yes they were created as a 
> seperate partition) however I am not sure if OpenLDAP or MySQL installs 
> anything to /usr which I would be completely screwed...
> Please help

Advice provided as-is.

Boot from a live CD using the CentOS 6.2 install media. Once booted:

<bash># grub
<grub> root (hd0,0)
<grub> setup (hd0)
<grub> root (hd1,0)
<grub> setup (hd1)
<grub> root (hd2,0)
<grub> setup (hd2)
<grub> quit
<bash># reboot

This assumes that grub sees the drives at '0, 1 and 2' and the boot
partition is the first on each drive. If it is, when you type 'root
(hdX,0)' it should report that a file system was found. The 'setup
(hdX)' will tell grub to write the MBR to the specified disk.

E-Mail:              digimer at alteeve.com
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