According to one general aspect, a system may include a plurality of data nodes. Each data node may include either or both of a first storage medium and a second storage medium that is slower than the first storage medium. Each data node may be configured to store a piece data in either the first storage medium or the second storage medium. The system may be configured to store a plurality of copies of an active piece of data within two or more data nodes. A fast copy of the active piece of data may be stored by a first storage medium of a first data node. One or more slow copies of the active piece of data may be stored by respective second storage mediums of one or more respective other data nodes.