While Spark is not intended for ETL per se, when I need to copy data from s3 to HDFS, I just use sc.textFile and sc.saveAsTextFile, in most of my use cases it does it pretty fast.

But Spark is mostly a computation engine replacing MapReduce (plus a standalone cluster management option). not an ETL tool.

I would look into other tools, such as https://projects.apache.org/projects/sqoop.html but I'm sure you know it already.