The FileTool can be used to split a large layout file into a collection of smaller layout files.
For splitting, the command line takes the form:
filetool [-set variables] -split split_args
This mode will write output files corresponding to the partitions of a square grid logically covering all or part of a specified cell in a given layout file. The output files contain physical data only. These files can be flat or hierarchical.
The operations and split_args are identical to those of the Xic !splwrite command (19.2.4).