Default directories

If you have changed any of the default directories during installation, make sure you have root access and set these properties:

commitlog_directory 

The directory where the commit log is stored. Default locations:

• Package installations: /var/lib/cassandra/commitlog
• Tarball installations: install_location/data/commitlog

For optimal write performance, place the commit log be on a separate disk partition, or (ideally) a separate physical device from the data file directories. Because the commit log is append only, an HDD for is acceptable for this purpose.