Numerous sources have confirmed that Evan Powell, CEO of Santa Clara-based Nexenta will step down today as CEO under undisclosed circumstances.  He assumes the position of CSO in the company and had served as its CEO since 2007.  Privately held and founded in 2005, the company brings an open philosophy to software-defined storage and uses its community model to become a storage force.  Network storage veteran Bridget Warwick also joins the company as its CMO, chief marketing officer.Nexenta has been making waves with major partnerships and touts over 5000 customers, with an emphasis in the finance sector.  Their total sales are approaching half