Run WRFDA using wrf_input or wrfout

[StanWang]

Hi everyone. I'm just curious about one question.
Since WRFDA can run on either wrf_input and wrfout, there seems to be two methods to do the cycle data assimilation:
1. run WRF normally, and run DA based on wrfout;
2. run WRF with write_input=.true., and generate the wrf_input file (restart file), then run DA on wrf_input.
Are the two options different on any aspects? Thanks a lot guys.