The scalability of Spark is certainly not as established as that of Hadoop. It's entirely anecdotal as I'm not in a position to share verifiable details, but I

The scalability of Spark is certainly not as established as that of Hadoop. It's entirely anecdotal as I'm not in a position to share verifiable details, but I know of several installations that run Spark on several-hundred-node clusters. They're certainly well into terabytes, if not in the neighborhood of petabytes.