Dwight Merriman and Kevin Ryan have had their hands in more than their share of high-profile Internet startups. There’s the retailer Gilt Groupe, the news website Business Insider, and DoubleClick, the advertising network that was acquired by Google in 2007 for $3.1 billion.

Those are tough acts to follow. But the duo believes that their current startup, a company few people have heard of, could be their biggest success yet: MongoDB, a maker of database software that powers some of the Web’s most trafficked websites, including Craigslist, eBay, and the New York Times.

In October, the company--a runner up for Inc.'s 2013 entrepreneur of the year--raised $150 million (its Series F round of funding), pegging its value at $1.2 billion, more than any other startup in New York City. The company has raised a total of $231 million to date, from investors like Union Square Ventures, Sequoia Capital, and T. Rowe Price. It’s part of a high-stakes game to become the leader in a disruptive new form of database architecture, known as document-based databases, or “NoSQL.”

To a layperson, the differences between NoSQL databases and more traditional architecture can seem cryptic. But for those who spend time building Web and mobile applications, the appeal is huge: Databases built using this kind of software can handle massive quantities of data cheaply and quickly. It's also relatively easy to update--ideal for Internet startups that like to release quick-and-dirty versions of new products and then constantly upgrade them, or those that see explosive growth in the number of users.

“The database market is $30 billion market, and this is the biggest disruption in 25 years,” says Merriman. “We think the opportunity is huge.”

So do competitors. Facebook has developed its own approach, called Cassandra. There are also other startups, like Couchbase, taking aim at the space with similar products.

MongoDB has settled on an open-source strategy. In 2009, the company (then known as 10gen) released an open-source version of its software, and shifted the company's business model to selling service and support. The strategy is akin to the one followed by RedHat, which sold service and support for Linux, the open-source operating system, in the 90s. To market the product, the company hosts conferences for the software around the world. So far, MongoDB has been downloaded more than 5 million times.

The cofounders have used their hundreds of millions in venture funding to beef up staff, engineers, technical support, and marketing and sales staff. Today the company has 350 employees, up from 80 two years ago. Merriman says he expects that number to continue to grow to more than 750 by the end of 2014. The company has more than 600 customers, including eHarmony, MetLife, Intuit, and Cisco. 

“My view on startups is that there are a series of risks,” says Merriman. “Can we build it? Is it any good? Do they like it? Will enterprises use it and not just startups?  There are a whole bunch of those challenges we've already passed. We just have to keep going.”      

Correction: An earlier version of this piece misstated the number of employees MongoDB expects to have by year end. The number is 350.  The story also misstated name of a competitor. It is Couchbase.