+ sync_min
+ sync_max
+ The two values, given as numbers of sectors, indicate a range
+ withing the array where 'check'/'repair' will operate. Must be
+ a multiple of chunk_size. When it reaches "sync_max" it will
+ pause, rather than complete.
+ You can use 'select' or 'poll' on "sync_completed" to wait for
+ that number to reach sync_max. Then you can either increase
+ "sync_max", or can write 'idle' to "sync_action".
+