Sometimes crazy changes need to be performed to adjust how storage is laid out and arranged. In this instance converting an existing (but non-critical) RAID1 mdadm array to RAID0 (even less critical) is the far-fetched requirement.
Every once in a while hardware needs to be replaced. Sometimes boards, sometimes CPUs and sometimes drives. Drives are the ones most difficult to replace as they hold all that precious data one does not want to lose.
I personally hate reinstalling stuff; so I try as much as possible to “migrate” my data around. In this tutorial I’ll be replacing two drives under a RAID1 array with two newer bigger drives (and resize the array accordingly).