[CentOS] Lost mdadm.conf

Les Mikesell lesmikesell at gmail.com
Thu Dec 31 17:19:53 UTC 2009

James Bensley wrote:
> 2009/12/31 Luciano Rocha <strange at nsk.no-ip.org>:
>> On Thu, Dec 31, 2009 at 11:39:25AM -0400, robert mena wrote:
>>> Hi,
>>> I lost my mdadm.conf (and /proc/mdadm shows nothing useful) and I'd like to
>>> mount the filesystem again.  So I've booted using rescue but I was wondering
>>> if I can do a command like this safely (i.e without losing the data
>>> previously stored).
>>> mdadm -C /dev/md0 --level=raid0 --raid-devices=2 /dev/sda1 /dev/sdb1
>>> Where of course the raid devices and the /dev/x are the correct ones
> 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, I thought mdadm.conf wasn't really necessary these days and if the 
partitions are type FD (autodetect) the md devices are assembled before you'd be 
able to read /etc anyway.  If your partitions aren't set to autodetect, you 
might be able to change that, reboot, and come up working.

> Use "sudo mdadm -E --scan" do get a list of discovered RAID devices
> like this example:
> ARRAY /dev/md0 level=raid0 num-devices=2 UUID=fde94900:3f3f3bf6
> Pop the results in your mdadm.conf and that should sort you out after
> a reboot (I think). Also try something like "sudo mdadm --assemble
> /dev/md1
> /dev/sdb1 /dev/sdc1" to assemble the RAID manually.

'cat /proc/mdstat' should show the status of the md devices and the partitons 
that are working so far.

   Les Mikesell
    lesmikesell at gmail.com

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