Hi Phil,
thanks for your help!

On 13.10.2011 23:09, Phil Turmel wrote:

You *do* understand that "linear" has *no* redundancy? If you can't 
read anything at all off the bad drive, that fraction of your data is 
*gone*. As a linear array, files that are entirely allocated on the 
other three are likely to be recoverable. 

Yes, 500GB are gone for sure. It's just about recovering what's left on 
the three working drives.

Create a zeroed placeholder file for the missing drive (must be exactly the right size):

dd if=/dev/zero of=Disk2_Partition3.fake bs=512 count=624353185

OK, one 500GB drive is dead (I had 2x320GB and 2x500GB), so I modified 
the line to
dd if=/dev/zero of=Disk2_Partition3.fake bs=512 count=$((499703758848/512))
because Partition 3 on that drive was 499703758848 bytes

mdadm --create --metadata=0.90 --level=linear -n 4 /dev/md0 /dev/loop{0,1,2,3}

I think I need --chunk=64 as well because mdadm defaults to 512kb and 
the Intel box uses 64kb?
http://www.intel.com/support/motherboards/server/ss4000-e/sb/CS-029880.htm

Best regards,
Johannes Moos