The data is processed and written tile-wise by default. The tile-size of the product is used when it is written.
Be default the tile size is 512x512. But this can overwrite each product reader separately.
You can specify the system properties snap.dataio.reader.tileWidth and snap.dataio.reader.tileHeight when you invoke the gpt.
e.g. -Dsnap.dataio.reader.tileWidth=* -Dsnap.dataio.reader.tileHeight=10 to write always chunks of 10 complete lines.
The asterisk means the full width or full height respectively .
Explicit write parameters are not yet supported but we have it on the agenda.