The following options are available.
memfrac - value between 0.1 and 0.8. The fraction of RAM that may be used by the program.
tempdir - directory where temporary files are written. The default what is returned by tempdir().
datatype - default data type. See writeRaster
filetype - default file type. See writeRaster
progress - non-negative integer. A progress bar is shown if the number of chunks in which the data is processed is larger than this number. No progress bar is shown if the value is zero