Sounds like you enabled some flow and based upon your current logging levels configured in your logback.xml you have insufficient disks space to sustain the amount of output being created.
You can reduce the log level via the logback.xml before restarting NiFi.
If the logging being produced is a result of a ERROR or WARN, you may want to restart your NiFi dataflow in a stopped state.
To do this change the following line in the nifi.properties configuration file before restarting NiFi:
Do not forget to change this property back to "true" later so your NiFi does not always startup in a stopped state.
With everything in a stopped state you can make dataflow adjustments and enable/start only select processors/components.