Nagy Zoltan wrote:

hi

quoted

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.

i feeled that there is another solution that i missed  - thank you, next 
time
i will do it this way -- because the system is already up and running, i 
don't wan't
to recreate the array (about the chunksize: i've got back to 64Kb chunks 
because
of that bug - i was happy to see it running ;)

quoted

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

okay - i've run thru the whole scenario a few times - and always come 
get back
to raid55, what would you do in myplace? :)

The validity of the snipped arguments depends on how many devices you have at 
every level:

*) how many nodes there are?
*) how many disks per node? do all nodes have an equal amount of disks?

Without additional info I would say this: The problem with using raid5 on the 
top node is that you are stressing your network additionally for every 
r-m-w-cycle. Also rebuild of this array, especially if you add more leaves 
will be more and more resource intensive.

In contrast if the top array is RAID10 with 2 chunk copies, you will sacrifice 
half the space, however your rebuild will utilize only 2 drives (one reader 
one writer).

HTH

Peter