Free implementation of the VMware cluster file system
fluid Operations, a provider of management software for complex fully virtualised environments, has developed an open source implementation of the VMFS cluster filing system that uses VMware ESX to store virtual machines and disks. This is a userspace driver written in Java that has been tested under Windows and Linux, but according to the project's site it "should work on any platform that supports Java". It only supports VMFS3, not versions 1 or 2, and was developed by analysing the on-disk format of VMFS.
At present, the software only permits read access to VMFS volumes, but that's enough for creating back-ups of virtual machines. Volumes can be mounted as a regular file system using the VMFS WebDAV server, based on the Jetty web server and Milton WebDav API. The driver also has a command line interface that allows users to mount and analyse VMFS volumes. The open VMFS driver, which is hosted on Google Code, is to be integrated into fluid Operations' eCloudManager.