RE Array size dropped from 40TB to 7TB when upgrading to 5.10

[Ian Kumlien <ian.kumlien@xxxxxxxxx>]

Hi,

the same thing happened to me, but it was a raid6...

Eventually I just gave up and did a:
mdadm --grow /dev/md3 --size=max (since it reflects the size it used to be)

After a few hours of syncing, everything was ok again
(according to btrfs check which also took a few hours =))

But remember to do this with a 5.0.1 kernel ;)