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.