From the introduction:
DuraSpace is envisioned as a service that acts as a mediator between institutional or end-user applications and a variety of 3rd party storage services. The purpose of the service is to provide a trusted intermediary that offers different levels of service toward making digital content (1) durable - meaning it is accessible for long periods of time, and thereby "preserved" and (2) usable - meaning that it can be re-exposed or dynamically transformed to fit within in a variety of application contexts. The core DuraSpace service manages storage and retrieval of content from multiple 3rd party storage providers (commercial "clouds" and enterprise/university "intra-clouds"). In addition, we envision a "chinese menu" of value-add DuraSpace services including preservation-motivated functions (replication of multiple copies, monitoring, reporting, migration) and access motivated functions (possibilities include bulk indexing, media streaming, Fedora/DSpace repositories in cloud, JPEG2000 engine, other TBD).
Update: DuraSpace is now DuraCloud. More information available here.