On 04/11/17 18:34, Reindl Harald wrote:

quoted

What's happened is that mdadm has assembled the array, realised a disk
is missing, AND STOPPED.

why would it be supposed that a simple mirror with a mising disk is 
stopped while the whole point of mirroring is to not care about one of 
the disks dying?

While the system is RUNNING, yes. But if the array is STOPPED, mdadm 
will refuse to start it. At least, that's certainly how I understand it 
works ...

Do you REALLY want the system to be running, and give you no clue that 
it's not working properly?

Cheers,
Wol