What does this ERROR message mean?

There was a problem writing in-memory hints to disk.

Why does this ERROR occur?

When writing hints to the hints_directory location defined in the cassandra.yaml, some disk or filesystem issue has occurred that prevents the hint from being written.

How do you fix this ERROR?

• Verify the hints_directory is accessible and Cassandra has permissions on the directory (see example below).

      drwxr-xr-x  2 cassandra cassandra 4096 Sep 21 18:49 hints
      

• Check operating system logs (e.g. /var/log/messages) for disk device issues.