hello user-man,
rootfs redundancy it uses two root filesystems, one designated rootfs A and stored in the usual filesystem partition, APP; the other designated rootfs B and stored in a new partition, APP_b, which located after APP on the disk.
rootfs redundancy supports independent creation and updates of these two filesystems, switching, and failover.
note, the partition names, i.e. APP and APP_b may not be changed.
thanks