create_on_open=bool Don't pre-setup the files for IO, just create open()
when it's time to do IO to that file.
+pre_read=bool If this is given, files will be pre-read into memory before
+ starting the given IO operation.
+
unlink=bool Unlink the job files when done. Not the default, as repeated
runs of that job would then waste time recreating the file
set again and again.