[CentOS] Expanding RAID 10 array, WAS: 40TB File System Recommendations

On 4/13/11, Rudi Ahlers <Rudi at softdux.com> wrote:
>> to expand the array :)
>
> I haven't had problems doing it this way yet.

I finally figured out my mistake creating the raid devices and got a
working RAID 0 on two RAID 1 arrays. But I wasn't able to add another
RAID 1 component to the array with the error

mdadm: add new device failed for /dev/md/mdr1_3 as 2: Invalid argument

Googling up this indicates that it's the expected result trying to add
a new device to a RAID 0 array. Could you or anybody else please share
what's the trick to achieving this?