Oh, I thought this was a backup system. I always ramp up the speed on
min & max to have the resync & reshapes finish fast, but at the loss
of performance during that.

	One of them, the one resyncing right now, is a backup system.  When
it is done, I will grow the main server.  I don't want to have both
performing potentially sensitive operations simultaneously.

You mentioned that you've unmounted the filesystem, so why does it
make a different if you max the speed? Or do you have other services
running?

	It probably doesn't matter on the backup, but the point is I would
rather not have it unmounted for the better part of 5 days.  I would rather
not go nearly 5 days without a valid backup, if I can avoid it.  Ordinarily
rsync runs every morning.

I think at the time I needed a new mdadm, I downloaded 3.0 which is
the stable one for now (3.1 was pulled -- donno about 3.1.1).

	Unless there is some compelling reason to download 3.0, I think I
will wait for it to be included in the stable distro of Debian.