ruthenium runs parsoid tests, specifically "visualdiff" tests.
They fill up /srv/visualdiff/png with lots of small files , several GB every once in a while.
This made ruthenium run low on disk, as everything was on the 40GB / mount.
We fixed that for now by mounting the un-used /dev/mapper/ruthenium-vg-tank with over 377GB free space.
But we still need proper logrotate for this added to the puppet role.