Configuring RAID 10 with RedHat ES 4 (64 bit)

[Stephen Carville]

On Wed, 18 May 2005, Andy Mountford wrote:

> Hi,
>
> I am trying to configure an array of 12 disks in a RAID 10
> configuration. All 12 disks are identical 146Gb drives.
>
> First off, on each disk I created a single partition which spanned the
> whole disk with a system id of 0xFD. After writing the partition
> table, a print confirmed all looked good.
>
> Secondly, I used mdadm to create 6 RAID 1 pairs. (mirrored).
>
> mdadm --create /dev/md0 --level=1 -n 2 /dev/sda /dev/sdb
> mdadm --create /dev/md1 --level=1 -n 2 /dev/sdc /dev/sdd
> mdadm --create /dev/md2 --level=1 -n 2 /dev/sde /dev/sdf
> mdadm --create /dev/md3 --level=1 -n 2 /dev/sdg /dev/sdh
> mdadm --create /dev/md4 --level=1 -n 2 /dev/sdi /dev/sdj
> mdadm --create /dev/md5 --level=1 -n 2 /dev/sdk /dev/sdl
>
> cat /proc/mdstat showed the devices syncing. Once this had completed I
> created a final meta device which striped the RAID1 meta devices. e.g.
>
> mdadm --create /dev/md6 --level 0 -n 6 /dev/md0 dev/md1 dev/md2
> dev/md3 dev/md4 dev/md5
>
> I could then create a filesystem on the new array and mount it - all
> looked good. However, 2 things concerned me:
>
> 1. After creating the RAID array, the partition table for all the
> disks involved was empty and an fdisk returned:
>
> "Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)"
>
> What's going on here?
>
> 2. How can I get the array to come up after a reboot? What needs to be
> done? Do I need an rc script that runs mdadm?

I had a similar problem with an AS3 box that has a large RAID 0 I'd built 
using mdadm.  Took me half a day to track it down.

The rc.sysinit script for AS3 does not check for mdadm.  It only looks for 
raidtab.  so....

Create an mdadm.conf file:

$ echo 'DEVICE partitions' > mdadm.conf
$ sudo mdadm --detail --scan --confin=mdadm.conf >>mdadm.conf
$ sudo c p mdadm.conf /etc/mdadm.conf

Add to rc.sysinit:

if [ -f /etc/mdadm.conf ]; then
         /sbin/mdadm -A -s
fi

I added it right before the line that checks for /etc/raidtab but YMMV.

--
Stephen