On Wed, May 24 2017, Nix wrote:
>
> (I'm not sure what to do if it *works* -- how do I test any later
> changes? I might reshape back to RAID-5 + spare again just so I can test
> later stuff, but that would take ages: the array is over 14TiB...)
>

If it works (which it did), then we'll have enough understanding that it
should be easy to simulate the problem accurately in a VM.
I don't think there is any need for you to experiment further on your
data.

Thanks,
NeilBrown