Slow on update

Hi,

I'm using DB version 11.1.0.7, recently I try to update a 10GB table, below is my statement:

update TEST_TAB set empid=empno;

There is 30mil rows in the table, this update take 1 hours to complete.

I try update by enable session parallel dml and adding parallel hints to the statement but it couldn't help, I seen parallel processes are sevicing this update, but just that it bring no benefit to the response time of the update, sometime I see it is running slower in parallel as compare to serial.

Any option or way that I have to get the update process more faster?