We have a csvloader, if you have file in a csv or tsv format - see https://docs.voltdb.com/UsingVoltDB/clicsvloader.php
. There is also a kafkaloader and jdbcloader, if you want to source data from kafka or from another database. You can also write client code to insert values. In most of our examples, you can see some values being loaded ( https://github.com/VoltDB/voltdb/tree/master/examples
) before or during the workload. The voltkv example starts up by preloading with randomly generated key,value pairs. There are examples of doing his using asynchronous, synchronous and JDBC clients.