We are getting low on disk for WDQS servers. This is being addressed in T196485. In the meantime, while looking at graphs, we see weekly increase in disk usage, at the same time as the reloadCategories.sh cron is scheduled. The increase seem to be between 5 and 20 GB each time. The latest categories .ttl.gz files are left on disk, but they are too small to explain this increase.
It looks to me like the old categories namespaces are not cleaned up.