Nagy Zoltan wrote:

hi all,

i've set up a two dimensional array:
   * leaf nodes composes raid5 arrays from their disks, and export it as 
a iSCSI target
   * the root node creates a raid5 on top of the exported targets

in this setup i will have to face that an array component can(and would) 
grow, so i
created a test case for this to see what comes out ;)
   * after growing the components mdadm won't recognized them anymore as 
an array member
       (because there are no superblock at the end of the device - last 
64k?)
      i've tried to inform mdadm about the size of the components, but 
it sad no ;)
   * i've added an arbitary superblock copy operation after the 
expansion, to make possible for
  mdadm to recognize and assemble the array - it's working, and passes 
my test.

is there a less 'funky' solution for this ;)
can i run into any trouble when doing this on the real system?

I would simply use a v1.1 superblock which will be situated at the start of
the array. Then you will face another problem - once you grow a leaf device,
mdadm will not see the new size as it will find the superblock at sect 0 and
will be done there. You will need to issue mdadm -A ... --update devicesize.
The rest of the operations are identical.

As a side note I am also curious why do you go the raid55 path (I am not very
impressed however :)

Peter