Check / Automatic repair

Hi,

I was reading the kernel md.txt documentation and found that couple of
sentences about sync_action :

496        check         - A full check of redundancy was requested and is
497                        happening.  This reads all block and checks
498                        them. A repair may also happen for some raid
499                        levels.


What levels/configurations are affected by the "A repair may also
happen for some raid levels." sentence ?

Regards