Having a look on the source, I'm confirmed, that the assembling problem
is related to the change indicated as:

   0cc3a8b md: Fix handling for devices from 2TB to 4TB in 0.90
metadata.

resp. to the following lines in drivers/md/md.c (Line 850ff):

--------------
850     rdev->sectors = rdev->sb_start;
851     /* Limit to 4TB as metadata cannot record more than that */
852     if (rdev->sectors >= (2ULL << 32))
853             rdev->sectors = (2ULL << 32) - 2;

--------------

Lines 851-853 where introduced in version 2.6.32-37.80


A further hint:
I operate also another data server with the same raid setup (two hardware raids 
merged to a raid0 md-raid), but with Ubuntu 12.04  on it (v 3.2.0-29). With 
this raid I didnt have any problems up to now.
Checking the source code of md.c for the respective part, I find the following:

-------------
        rdev->sectors = rdev->sb_start;
        /* Limit to 4TB as metadata cannot record more than that.
         * (not needed for Linear and RAID0 as metadata doesn't
         * record this size)
         */
        if (rdev->sectors >= (2ULL << 32) && sb->level >= 1)
                rdev->sectors = (2ULL << 32) - 2;
-------------

here, the 4 TB limit is only valid for raid levels above 1 ("&&
sb->level >= 1")

In summary:

-> introducing the 4 TB limit in general leads to problems for my large raids
-> limiting the 4 TB limit to raid levels above 1 seems to solve the problem 
(as I use raid level 0)

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https://bugs.launchpad.net/bugs/1247064

Title:
  mdraid not assembled correctly when booting from kernel newer than
  2.6.32-33

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