Enabling incremental backups 

Steps to enable incremental backups. When incremental backups are enabled, Cassandra hard-links each memtable flushed to a SSTable to a backups directory under the keyspace data directory.

When incremental backups are enabled (disabled by default), Cassandra hard-links each memtable-flushed SSTable to a backups directory under the keyspace data directory. This allows storing backups offsite without transferring entire snapshots. Also, incremental backups combined with snapshots to provide a dependable, up-to-date backup mechanism. Compacted SSTables do not create hard links in the backup folder because a snapshot will include links to SSTables that can reconstitute any compacted SSTable. A snapshot at a point in time, plus all incremental backups and commit logs since that time form a compete backup.

As with snapshots, Cassandra does not automatically clear incremental backup files. DataStax recommends setting up a process to clear incremental backup hard-links each time a new snapshot is created.

The location of the cassandra.yaml file depends on the type of installation:
Package installations /etc/cassandra/cassandra.yaml
Tarball installations install_location/resources/cassandra/conf/cassandra.yaml

Procedure

Edit the cassandra.yaml configuration file on each node in the cluster and change the value of incremental_backups to true.