Mirantis, which offers a commercial OpenStack distribution, has raised a $100 million Series B round. It's the largest Series B in open source history, Mirantis claims. That's pretty easy to believe.

The money — five times the amount of Mirantis' Series A, which completed in June 2013 — will go toward a doubling of Mirantis' engineering, the company said in today's announcement. Mirantis CEO Adrian Ionel also told GigaOm that the company will prep for a possible 2016 IPO.

OpenStack would be about 6 years old by then. While it's trendy and possibly accurate to cite OpenStack's relative immaturity, there's no question the open-source software has established a position in operators' roadmaps. It's also likely to play a role in orchestration for network functions virtualization (NFV), controlling pools of resources. (NFV is going to lead a higher layer of orchestration on top of that, however.)

Of course, large funding rounds can also be the glimmer of an investment bubble. While OpenStack has certainly reached a point of acceptance, we'll have to see whether Mirantis' investors are truly funding the future or just overdoing it. (The former is possible. Red Hat, which admittedly does a whole lot more than OpenStack, has a market capitalization of more than $10 billion.)

The round was led by Insight Venture Partners and also included new investor August Capital and prior investors Intel Capital, WestSummit Capital, Ericsson (which signed a $30 million, five-year license with Mirantis in April), and Sapphire Ventures. Alex Crisses of Insight Venture Partners is joining Mirantis' board.