[CentOS] Lost mdadm.conf

Thomas Harold thomas-lists at nybeta.com
Fri Jan 1 22:20:58 UTC 2010

On 12/31/2009 11:27 AM, James Bensley wrote:
> I can't say this with 100% certainty but I would of thought that it
> would been fine. I've lost my mdadm.conf (reinstalled OS) with a
> separate 4 disk RAID 5 array and re-assembled the array and carried on
> as if nothing had happened.

Yes, in general, you don't need the mdadm.conf at all.  As long as the 
array is built out of partitions marked as type "fd: Linux raid autodetect".

However, whenever CentOS installs a new kernel and initrd image file, it 
creates (or uses?) an mdadm.conf file within the initial boot 
environment.  Back when I was migrating a server to a new environment, I 
had to unpack the image, edit that copy of mdadm.conf, and then repack 
it all in order to get a proper boot.

So I suspect (but am not certain) that the ARRAY lines in 
/etc/mdadm.conf are useless on a CentOS system but that the ARRAY lines 
inside the initrd image file are the real ones used.  But the former may 
be used to generate the latter when you install a new kernel.

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