If you just want to generate tiles and not update them then you can import Europe, generate tiles for that, throw that away, import North America, generate tiles for that, etc. That will mean that you don’t need to have hardware in place to handle the whole planet at once, but you’ll either still need quite a large server (for the larger continents) or lots of iterations (country by country).
As you’re only interested in up to zoom 11 you could edit your chosen style to not reference any features only displayed from z12 and above, and also edit the project.mml and osm2pgsql style file to neither extract not process data that you’ll never see. In addition you can use osmfilter to remove from the data that you import things that you are not interested in. However, this all requires a level of familiarity with osm2pgsql and carto-based style files that you probably do not have yet.
Thanks for your information. Looks like a good idea to import smaller planet areas instead of the whole planet and render the tiles area by area. But first I need to get to the point where I’m actually able to pre-generate raster tiles - that look good. On my first tries, I only got water color and white land area. The reason for that was probably because I did not use generate_xml.py before using generate_tiles.py. Now it’s starting to look like a map, but things get misaligned, lots of roads missing etc.