/MIR this will MIRror a directory tree - whatever exist in source, will be copied to target. Whatever does not exist in source, will be removed (deleted) from target. By this option you will make sure, that no old data (those already removed on source) will be migrated to new server. This option is equivalent to /E plus /PURGE.
/COPY:DATSOU copies everything (same as /copyall)
/ZB if copy of a big file is interrupted robocopy automatically switches to 'backup' mode and repeats copying the file
/R maximum amount of errors to occur before stopping the copy process
/W seconds to wait before retrying to copy a file again
/TEE displays everything in cmd
/NP percentage is not logged (otherwhise the log would be full of % signs)