Are you sure you didn't have an additional hot-spare previously, that has already been used for the raid rebuild? Does your array (under Pools \ Mdisks by Pool in GUI) show a status of Online or Degraded? Are there "array mdisk rebuild started/completed" events in your Event Log?
Use "lsarray" command to show your list of configured RAID arrays, and then view use of each individual drive in your array/mdisks using CLI command "lsarraymember". If you're still not sure where your failed drive/spare drive status is at, post output of above two commands in thread.#Storwize#Support#SupportMigration