I poked through the source code and found that there is some effort to update the superblock to "revert-reshape”, using the assemble command but: 1. Most systems assemble my arrays on my behalf 2. I was trying to back out of a reshape on a turnkey NAS, and couldn’t figure out how to mount the target filesystem 3. I tried sudo echo revert-reshape > /sys/block/md2/md/sync_action #and got echo: write error: Device or resource busy Ideally since I can start a reshape on an array while it’s hot it would make sense to be able to back out of it by syncing up and then doing the transformation in reverse without needing to take it offline. I would prefer a user friendly way to do this where all I need to do is mdadm -G —cancel /md/mdX
