'no space left on device' Drupal warning messages

From irc:

<snoek> Not sure where to put this info, as there's no #tor-it channel, but
when I was browsing the events calendar on the tor blog, the site is
displaying 'no space left on device' Drupal warning messages: "Warning:
mkdir(): No space left on device in Drupal\Component\..."

I'm not able to reproduce immediately, but that doesn't mean there isn't some thing somewhere that's full and needs attention.