Enterprise cloud storage company Box.net is raising new venture capital funding at a pre-money valuation north of $500 million, Fortune has learned.

The company first disclosed the round earlier today in a regulatory filing, which showed that it had secured $18.6 million of a $35 million Series D-1 round. A source familiar with the situation says that the $18.6 million comes from insiders plus one new investor, while the company is still deciding on which new investors to bring in for the remainder. He adds that Box.net chose to make this a Series D-1 round rather than a Series E round in order to maintain existing voting rights.

Box.net previously raised $45 million in Series D funding six months ago, although $10 million of that amount was a credit line that the company has not yet tapped. Participants on that round included new investors Andreessen Horowitz, Emergence Capital Partners and Meritech Capital Partners, plus returnees like Draper Fisher Jurvetson, Scale Venture Partners and U.S. Venture Partners.

At the time, part of the proceeds were to be used for doubling the company’s workforce. I’m told that process is nearly complete, even though Box.net still has around half of its venture dollars still in the bank.

“The company could keep growing organically without extra money, but they now have around 200 employees and 100% year-over-year revenue growth,” our source says. “This will help them meet that demand, and grow aggressively.”