Cloud storage startup Symform has raised $2 million in equity funding from West River Capital.

Seattle-based Symform, co-founded by former Microsoft managers Praerit Garg and Bassam Tabbara, has now raised $7.5 million.

The company says it has users in 46 countries storing more than 2 billion data packets and has seen revenue, partners and users grow rapidly over the past year.

Symform offers small businesses a unique way to implement cost-effective data backup services, with an operating a system that lets customers turn over unused storage capacity on their servers in exchange for online backup services.

Symform storage users also can receive up to 200GB of free cloud storage for registering, contributing and referring friends or colleagues.

"Current cloud storage prices are not economical, reaching nearly $1,000 a month on average. We are in the midst of a storage revolution whereby businesses are in need of a much more cost-effective option, but current providers are stymied by the limitations of traditional, centralized datacenter approaches for cloud storage and backup," said CEO Matthew Schiltz.

In 2010, the company landed $4 million in venture capital from Longworth Venture Partners and OVP Venture, part of an overall funding of $5.5 million.