Run out of Space during importing with osm2psql


my problem is, that my indexing process from osm2psql is failing, because it is running out of disk space.
I have running folloging Hardware:
Processor: i7 with 3,5 Ghz
RAM: 32 GB
HDD: 2x 500 GB SSD as RAID1

Operating system: Ubuntu Server 16.04 LTS
When I start with the indexing, there are 420 GB available.
Readed file: planet-latest.osm.pbf from 2 Weeks ago.

At last I tried id with this command:

osm@map:~$ osm2pgsql --slim --drop -d gis -C 20000 --hstore --flat-nodes slimcache/nodes.cache -S openstreetmap-carto-2.41.0/ planet-latest.osm.pbf

The system run. After round about 20h it stopped. I think it seems it is nearly finished.
Last successfull finished step is:

Going over pending ways...
        260052692 ways are pending

I want the possibility to update ist later.
Any Ideas how I can perform it. That I didn’t run out of space?
I thought a System with 500 GB SSD would be enough space.

Thanks a lot.

420 GB is not enough for the full planet (unless you use a really simple style that drops most things).
My rendering-DB currently is 521 GB on disk.
Plus 35 GB for the flatnodes-file. You did use flatnodes hopefully? If not, you will certainly want to enable that - it both saves space and speeds up processing.