question: public void takeColumnFamilySnapshot ( String keyspaceName , String columnFamilyName , String tag ) throws IOException { if ( keyspaceName == null ) throw new IOException ( "You must supply a keyspace name" ) ; if ( operationMode == Mode . JOINING ) throw new IOException ( "Cannot snapshot until bootstrap completes" ) ; if ( columnFamilyName == null ) throw new IOException ( "You must supply a table name" ) ; if ( columnFamilyName . contains ( "." ) ) throw new IllegalArgumentException ( "Cannot take a snapshot of a secondary index by itself. Run snapshot on the table that owns the index." ) ; if ( tag == null || tag . equals ( "" ) ) throw new IOException ( "You must supply a snapshot name." ) ; Keyspace keyspace = getValidKeyspace ( keyspaceName ) ; ColumnFamilyStore columnFamilyStore = keyspace . getColumnFamilyStore ( columnFamilyName ) ; if ( columnFamilyStore . snapshotExists ( tag ) ) throw new IOException ( "Snapshot " + tag + " already exists." ) ; columnFamilyStore . snapshot ( tag ) ; }
target:  Takes the snapshot of a specific column family. A snapshot name must be specified.