Using the command line interface (CLI) : execute : execute raid rebuild
 
execute raid rebuild
The execute raid rebuild command allows you to rebuild the hard disk raid when the raid is corrupted.
Syntax
execute raid rebuild
 
Rebuild raid will clean all exist data in 2nd hard disk.
If you just replace the 2nd disk from exist raid, the new inserted disk will get raid synchronizing automatically and does not need rebuild raid. But if the 2nd disks was part of raid volume before, usually need rebuild it.