[CentOS] RAID 1 not boot when disconnect a disk

Kevan Benson kbenson at a-1networks.com
Sat Nov 25 00:36:05 UTC 2006

On Friday 24 November 2006 09:53, Aleksandar Milivojevic wrote:
> Quoting Roberto Pereyra <pereyra.roberto at gmail.com>:
> > Hi
> >
> > I have a clean CentOS 4.4 disk and I have setup a RAID 1 with two  IDE
> > disk.
> >
> > The system RAID 1  boot fine  but when I disconnect a disk (the first
> > disk) the system not boot. The screen goes black and not boot anything
> > (grub not boot).
> Where is the Grub installed?  MBR or partition?
> If you've setup RAID-1 during installation, Anaconda should have
> installed it in partition, which would mean that it got automatically
> mirrored to second drive.  If this is the case, most likely your BIOS
> is refusing to boot from second drive.  Also check that partition that
> holds /boot (usually first partition on the disk) is marked as
> bootable (use fdisk).

Unless it's new in 4.4, that's not the case.  Grub can't undertand the md 
devices, and has to be installed on the disk geometry individually, as your 
link suggests, which anaconda doesn't do.  I hear RHEL 5 fixes this though.

In other words, if you want software RAID-1 with either disk bootable, follow 
the directions on the link you posted in every case, not just when adding 
RAID after install.

> If you've installed on single drive, and setup RAID-1 after
> intallation manually chances are Grub is installed in MBR of first
> drive (Anaconda defaults to install Grub into MBR when installing on
> single drive).  If that is the case, than it won't be automagically
> mirrored to second drive.  You'll have to install it into second
> drive's MBR by hand, for example:
> http://www.8-p.ca/archives/3-Grub-and-RAID-1.html

- Kevan Benson
- A-1 Networks

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