Cloud computing firm Rackspace has sued two US firms, Parallel Iron and IP Nav for breach of contract saying that they are ‘most notorious patent trolls in America’.

The company has also sought a federal court intervention for a declaratory judgement that it did not infringe three patented technologies owned by one of the firms, Parallel Iron.

In December 2010, IP Navigation Group (IPNav) sued Rackspace alleging that its patented technologies on storage-area-network (SAN) and network-attached-storage (NAS) equipment also covered the open-source Hadoop distributed-file system (HDFS) deployed by Rackspace.

Both the firms then signed a "forbearance agreement," which assumed that either side would give the other 30 days notice before suing each other.

Further, Rackspace alleged Parallel Iron of breaking the agreement by suing Rackspace without giving any prior notice.

Rackspace senior vice president, general counsel Alan Schoenbaum alleged patent trolls like IP Nav are a serious threat to business and to innovation.

"Patent trolls brazenly use questionable tactics to force settlements from legitimate businesses that are merely using computers and software as they are intended," Schoenbaum said. "These defendants, including most of America’s most innovative companies, are not copying patents or stealing from the patent holders. They often have no knowledge of these patents until they are served with a lawsuit. This is unjust."