I've got 2 sources of entropy in my CentOS7 system, a hardware RNG and the Intel rdrand instruction. Is it advisable to just use a single source or can/should I mix the 2 sources?

If I mix the 2 sources how is it done? Presumably I could use the rngd service to handle the Intel source, but would it be a problem if 2 entities were writing to the entropy pool?

Thanks.