osm2pgsql import - disk space running out during index creation

When I am trying to import a Europe pbf file with osm2pgsql, my diskspace keeps running full during the index creation.

After the import of nodes, ways and relations the tablespace of the database has a size of 233 GB and there is still 244GB disk space available. But during index creation, these 244GB are completely used up. When I imported a europe data set one year ago, the disk space was enough for the database + the prerendered tiles.

Any suggestions as to why the index creation might use up so much disk space this time? Is this normal?

I'm using the following import command:

nohup osm2pgsql ~/osm/europe-latest.osm.pbf --create --slim --database gis --number-processes=4 --cache=22000 --multi-geometry --flat-nodes ~/osm/flat-nodes.bin

And the following postgres config:

shared_buffers 8 MB
work_mem 1 MB
maintenance_work_mem 4096 MB
fsync off
autovacuum off
checkpoint_segments 60

My Stack: Mod_tile, renderd, mapnik, osm2pgsql and a postgresql/postgis database.

Maybe it's worth mentioning that the system has 4CPU and 16GB RAM, with another 16GB of SWAP space.

This is the error message in the log file:

Creating geometry index on  planet_osm_polygon
pthread_join() returned exception: Throw location unknown (consider using BOOST_THROW_EXCEPTION)
Dynamic exception type: boost::exception_detail::clone_impl<boost::exception_detail::current_exception_std_exception_wrapper<std::runtime_error> >
std::exception::what: CREATE INDEX planet_osm_polygon_index ON planet_osm_polygon USING GIST (way)   failed: ERROR:  could not extend file "base/16385/8687919.15": No space left on device
HINT:  Check free disk space.
St13runtime_error
Error occurred, cleaning up