When setting an environment variable gives you a 40x speedup
It may be worth mentioning that this sort of thing isn't just a problem for whoever is running it, because it may have a bad effect on other users if you hammer the metadata server(s). It's necessary to have monitoring which can identify the jobs responsible and take action. The Lustre system here was clobbered for several days because the admins had no means of doing that, despite all the facilities provided for and by Lustre.