RAID 0+1 (Problem)

[Daniel Buggie]

ECJ wrote:

>Hello All,
>
>I followed the steps in the link below but my RAID 10 array had a problem
>after a reboot.
>What I did was:
>- constructed 2 RAID0s (3x73GB each)
>- combined these 2 into a RAID1
>- mkfs.ext3 /dev/md45 (the name of my RAID10 array)
>- mounted it on /data
>
>All seemed ok. It shows on /proc/mdstat. Can write to the partition where
>I mounted it. But after a reboot, I got errors re this new RAID device and
>was  prompted for the root password to enter repair mode.
>Is there something I am missing here?
>
>  
>
Did some tests, and was able to replicate your problem so hopefully this 
will work on your system.

First, make sure the  OS can start the RAID-0's. If it can, see if you 
can start the RAID10 with:
mdadm -As /dev/md45

If you get something like:
mdadm: no devices found for /dev/md45

Then the problem is your mdadm.conf file. In that case, run:
mdadm --examine --scan /dev/md4 /dev/md5 >> /etc/mdadm.conf

And for some reason, it didn't like the devices= field on my system, so 
get rid of those and replace it with a "DEVICE partitions" line at the 
very top of the file.

If you can then do the mdadm -As command, you should be good to go. 

And definitely talk to your boss about WHY he wants mirrored stripes.  
If its for 'performance reasons' offer to bench the two and that should 
show him that any performance difference would be statistically 
insignificant and not worth the loss of redundancy. Having numbers to 
back up your case may help.

Hope this helps,

Daniel