Robocopy log file

I use the following robocopy command to copy files from old to a new server:

@ECHO OFF

SET _source=d:\data\
SET _dest=\\newserver\DATA\

SET _what=/COPYALL /ZB /secfix /SEC /MIR

SET _options=/R:0 /W:0 /LOG:C:\MyLogfile.txt 

ROBOCOPY %_source% %_dest% %_what% %_options%

How can i change this command to only log changes new files and directories.  Right now is logging everything.

Thanks

patyk