geoserver terrain provider progress

I'm trying to implement a geoserver terrain provider. I made a image Pyramid with ( -v -r lanczos -levels 6 -ps 2048 2048 -co "TILED=YES" -co "COMPRESS=DEFLATE" -co "ZLEVEL=4" -ot Int16 -targetDir pyramid *.tif) from SRTM 250meters.
My git repository is :

Problems: I can't above level 4 without glitches

PS How can I add images to illustrate the glitches in he forum?