On 22/07/2022 10:57, Nix wrote:

I thought all the work done to assemble raid arrays was done by mdadm?
Because that didn't change. Does the kernel md layer also get to say
"type wrong, go away"? EW. I'd hope nothing is looking at partition
types these days...

As far as I know (which is probably the same as you :-) the kernel knows 
nothing about the v1 superblock format, so raid assembly *must* be done 
by mdadm.

That's why, despite it being obsolete, people get upset when there's any 
mention of 0.9 going away, because the kernel DOES recognise it and can 
assemble those arrays.

Cheers,
Wol