1. Concept: Well-managed provisioning of storage space on OSG sites owned by large communities, for usage by other science communities in OSG. Examples –Providers: CMS, ATLAS. –Consumers: D0, CDF, …, DES, SBGrid. Opportunistic Storage on OSG

2. Procedure A provisioning site implements the model, makes space allocations when needed, and advertises the ‘token’ to the consumer VO. Technological model leverages on: –Space reservation functions in SRM v2.2 spec. –If applicable at a site, dCache filesystem internals and disk partitioning. Space allocation at a storage site: –Based on a formal understanding between provider and consumer. –Allocation made with a well-defined size and lifetime. E.g., 1 TB for 1 year. –Space expected to expire after the due lifetime.

3. Technology Areas in need of Improvement Token lifetime flexibility: In current implementations, altering the lifetime of a token is not possible. This can lead to unintended expiration of tokens, and loss of data in the expired space. This flexibility will be required for re-negotiation of space allocations. Token access control consistency: If a token identifier is widely known, there is a potential of VOs' writing into their own areas - by using another VO's token. Strict access control over space allocations will be required for wider usage of opportunistic storage. Token advertisement: Within limitations of token access control, dynamic mechanisms to advertise tokens using Generic Information Provider (GIP) will be useful for wider deployment of opportunistic storage. Pure opportunistic throttles: If a site does not perform a physical partition, separating subsets of disks, there is a risk of opportunistic load overlays -- disk I/O, CPU load, and network I/O overlays -- taking a toll interfering with the main provider’s own transfers. Overall, not a major problem in the short-term. In long term, however, new internal mechanisms for separation of data-mover queues on a per-VO-basis or a per-token-basis will be required on disks.

4. D0’s Needs D0 typically submits 60,000-100,000 jobs per week at 20-25 sites on OSG. The experiment’s workflows make multiple requests for input data in quick succession. In past, due to lack of storage local to the processing sites, D0 input/output data had to be transferred in real time over the wide area network. This had led to high latencies, job timeouts, job failures, and excessively low overall efficiencies.

5. D0’s Solution D0 started using opportunistic storage in Summer’08. D0 and OSG worked together to make changes in D0’s workflow to adapt to SRM client-side usage. Main providers –CMS: Tier-2’s at UCSD, UNL, Purdue. –ATLAS: MidWest Tier-2 at IU, Great Lakes Tier-2 at MSU:. Results: –Ready availability of space for data movement and storage. –Increase in D0’s workflow success rate. –Increase in D0’s efficiency of OSG wall hours utilization. –Increase in D0 Event production.