CentOS - Dec 2009 - Lost mdadm.conf

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
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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've collected an howto somewhere from the 'net:

$ cat docs/sysadm/mdadm_recovery.txt

## define possible devices with arrays
echo 'DEVICE /dev/hd[a-l]* /dev/sd[a-l]*' > mdadm.conf

## scan
mdadm --examine --scan --config=mdadm.conf >> mdadm.conf

## review configuration, copy to /etc
cp mdadm.conf /etc/

## create devices
MAKEDEV md || { for ((i=0; i <= 31; i++)); do mknod /dev/md$i b 9 $i;
done; }

## start arrays
mdadm --assemble --scan

Best of luck,

-- 
lfr
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>I've collected an howto somewhere from the 'net:
>
>$ cat docs/sysadm/mdadm_recovery.txt
>
>## define possible devices with arrays
>echo 'DEVICE /dev/hd[a-l]* /dev/sd[a-l]*' > mdadm.conf
>
>## scan
>mdadm --examine --scan --config=mdadm.conf >> mdadm.conf
>
>## review configuration, copy to /etc
>cp mdadm.conf /etc/
>
>## create devices
>MAKEDEV md || { for ((i=0; i <= 31; i++)); do mknod /dev/md$i b 9 $i;
done; }
>
>## start arrays
>mdadm --assemble --scan
That's a fairly limited script and out of date, I've never used mknod...

Simply:
# mdadm --detail --scan --verbose
And look it over, then:
# mdadm --detail --scan --verbose > /etc/mdadm.conf

And worry about mountpoints etc now...

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.

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.

-- 
Regards,
James ;)

Pablo Picasso  - "Computers are useless. They can only give you
answers." - http://www.brainyquote.com/quotes/authors/p/pablo_picasso.html