VMware has agreed to buy 4 million Terremark shares at US$5 per share, a $0.20 premium on Terremark's closing share price Tuesday. The investment is valued at $20 million, the company said.

"VMware and Terremark have worked together for years, with VMware's software being a key component of our suite of virtualized offerings," said Manuel Medina, Terremark's chairman and CEO, in a conference call Tuesday.

"We look forward to continuing our long relationship with VMware as we develop reliable and scalable virtualization solutions for enterprise and federal customers," he said.

Terremark rents data-center capacity to third-party organizations. Customers can manage their own hardware at its facilities or sign up for managed hosting services using Terremark's equipment. Terremark uses VMware's virtualization software to run those managed services.

The companies are already close partners, with VMware naming Terremark as its "service provider of the year" for 2009. Their relationship appears set to get closer.