Force your md array to recheck parity from time to time, to assure data consistency. The following command will read every block on every disk in the md0 array:

echo check > /sys/block/md0/md/sync_action

The command will proceed in the background and respect other accesses to the block device by slowing down, just like regular md resyncs do. You can monitor progress in /proc/mdstat pseudo-file.