[CentOS] Booting Software RAID

SilverTip257
Fri, 24 Jan 2014 17:08:49 -0000

On Fri, Jan 24, 2014 at 11:58 AM, Matt <matt.mailinglists at gmail.com>
wrote:

> I installed Centos 6.x 64 bit with the minimal ISO and used two disks
> in RAID 1 array.
>
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/md2         97G  918M   91G   1% /
> tmpfs            16G     0   16G   0% /dev/shm
> /dev/md1        485M   54M  407M  12% /boot
> /dev/md3        3.4T  198M  3.2T   1% /vz
>
> Personalities : [raid1]
> md1 : active raid1 sda1[0] sdb1[1]
>       511936 blocks super 1.0 [2/2] [UU]
> md3 : active raid1 sda4[0] sdb4[1]
>       3672901440 blocks super 1.1 [2/2] [UU]
>       bitmap: 0/28 pages [0KB], 65536KB chunk
> md2 : active raid1 sdb3[1] sda3[0]
>       102334336 blocks super 1.1 [2/2] [UU]
>       bitmap: 0/1 pages [0KB], 65536KB chunk
> md0 : active raid1 sdb2[1] sda2[0]
>       131006336 blocks super 1.1 [2/2] [UU]
>
> My question is if sda one fails will it still boot on sdb?  Did the
> install process write the boot sector on both disks or just sda?  How
> do I check and if its not on sdb how do I copy it there?
>

I've found that the grub boot loader is only installed on the first disk.
When I do use software raid, I have made a habit of manually installing
grub on the other disks (using grub-install).  In most cases I dedicated a
RAID1 array to the host OS and have a separate array for storage.

You can check to see that a boot loader is present with `file`.

~]# file -s /dev/sda
/dev/sda: x86 boot sector; partition 1: ID=0xfd, active, starthead 1,
startsector 63, 224847 sectors; partition 2: ID=0xfd, starthead 0,
startsector 224910, 4016250 sectors; partition 3: ID=0xfd, starthead 0,
startsector 4241160, 66878595 sectors, code offset 0x48

There are other ways to verify the boot loader is present, but that's the
one I remember off the top of my head.

Use grub-install to install grub to the MBR of the other disk.


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--
---~~.~~---
Mike
//  SilverTip257  //