Hi, Peter. I think the problem is that the raid system looks for raid
devices in 'DEVICE partitions' by default as it's auto-detecting arrays.  
But you need it to also look in some raid devices themselves for another
array. Here's an /etc/mdadm.conf from one of our systems with a raid10
defined. In this case, md6 is the raid10, and md[4,5] are the sub-mirrors.
The key lines for autodetecting the raid10 at boot are the 'DEVICE
/dev/md4 /dev/md5' and the 'ARRAY /dev/md6 ...' one. The UUID, or some
other identifying information, can be had IIRC via something like:

mdadm --misc --query --detail /dev/md6

That assumes that the array is started, though. If you've lost it via a 
reboot and can't get it back online, I think you can do something like:

mdadm --misc --examine /dev/md4

(note that in the --examine case we're looking at one of the sub-mirrors).

DEVICE partitions
DEVICE /dev/md4 /dev/md5
ARRAY /dev/md0 super-minor=0
ARRAY /dev/md3 super-minor=3
ARRAY /dev/md2 super-minor=2
ARRAY /dev/md1 super-minor=1
ARRAY /dev/md4 super-minor=1
ARRAY /dev/md5 super-minor=1
ARRAY /dev/md6 level=raid0 num-devices=2 UUID=86c93314:62a7eba4:a1a8b392:72f89a69
   devices=/dev/md4,/dev/md5

-Jan

On Fri, 10 Nov 2006 [log in to unmask] wrote:

> Date: Fri, 10 Nov 2006 19:56:43 +0100
> From: [log in to unmask]
> To: [log in to unmask]
> Subject: Raid10 with SL 4.2
> 
> Hi,
> 
> I created a RAID10 out of 2 RAID1 arrays on a SL4.2 system with SCSI disks:
>    mdadm --create --force /dev/md11 --verbose  --level=raid1 --raid-devices=2
> /dev/sdb1 /dev/sdi1
>    mdadm --create --force /dev/md12 --verbose  --level=raid1 --raid-devices=2
> /dev/sdc1 /dev/sdj1
>    mdadm --create --force /dev/md10 --verbose --chunk=64 --level=raid0
> --raid-devices=2 /dev/md11 /dev/md12
> This RAID10 array is assembled and usable, but when I reboot the system, only
> the underlying RAID1 arrays are assembled, the RAID10 array is not.
> 
> Can anybody help me?
> 
> Best regards
> 
> Peter
> 
>  	Dr. Peter Stauffert
> 	Boehringer Ingelheim Pharma GmbH & Co. KG
> 		e-mail: [log in to unmask]
> 
> 
>