Also, in order for the open-e system to see a change in the number of disks, you have to do a unit rescan. After removing a disk and inserting it back again, it gets a new "Unit" name. For instance, if it originally was "Unit S002," it may become "Unit S003" when put back in. Then, after doing that unit rescan, you just add it as a hot spare for the appropriate (degraded) RAID array, then it will immediately start rebuilding. For me, rebuilding starts out at over 50MB/s at first and eventually at the end is closer to 30MB/s.
Robotbeat, Thanks for the help!
We appreciate all your great work!