Recently I've been asked to setup some VMWare VSphere servers (free edition) implementing some kind of backup of the virtual machines on a secondary server. The choice for secondary server was Openfiler - compared to FreeNAS (I tested both) looked definitively more robust and stable. I configured all VMWare hosts had a secondary storage (NFS) mounted from Openfiler, to easily perform backups on the Openfiler storage. Setting up the backup scripts was quite easy - you just need to google around