It's a combination of bandwidth and latency. Latency in particular feels slow; you need to copy the new binary on every node, then issue commands over ssh to sc

It's a combination of bandwidth and latency. Latency in particular feels slow; you need to copy the new binary on every node, then issue commands over ssh to scrub any previous leftover files, initialize a cluster, run the tests, stop the cluster, retrieve the log files. Doing all this over the network is just taking a few more seconds which makes running hundreds of tests much longer than they would locally.