Armin, This is a "well known" performance issue with the geotiff driver / libtiff when switching back and forth between IFD (image file directories). At ~ 75%, you start generating overview factor 4 and that implies switching regularly between the one previously computed (read operations) and the new one (write operations). Each time you switch, you need to read and write the TileOffsets and TileByteCounts tags (those can be 10's of megabytes large on huge file, and are the root cause for the performance problem). With infinite patience, this would eventually complete.
A trick you can use is : gdaladdo -ro --config COMPRESS_OVERVIEW LZW INPUT_FILE 2 gdaladdo -ro --config COMPRESS_OVERVIEW LZW INPUT_FILE.ovr 2 gdaladdo -ro --config COMPRESS_OVERVIEW LZW INPUT_FILE.ovr.ovr 2 gdaladdo -ro --config COMPRESS_OVERVIEW LZW INPUT_FILE.ovr.ovr.ovr 2 Even -- Spatialys - Geospatial professional services http://www.spatialys.com
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