In 1989, the RAID (Redundant Arrays of Inexpensive Disks) group at U.C. Berkeley built a prototype disk array called RAID-I. The bandwidth delivered to clients by RAID-I was severely limited by the memory system bandwidth of the disk array's host workstation. They designed their second prototype, RAID-II, to deliver more of the disk array bandwidth to file server clients. A custom-built crossbar memory system called the XBUS board connects the disks directly to the high-speed network, allowing data for large requests to bypass the server workstation. RAID-II runs Log-Structured File System (LFS) software to optimize performance for bandwidth-intensive applications. The RAID-II hardware with a single XBUS controller board delivers 20 megabytes/second for large, random read operations and up to 31 megabytes/second for sequential read operations. A preliminary implementation of LFS on RAID-II delivers 21 megabytes/second on large read requests and 15 megabytes/second on large write operations.>

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Data striping is a technique for increasing the throughput and reducing the response time of large accesses to a storage system. In this paper, we evaluate the effectiveness of applying striping concepts to large tape libraries. Striping in tape libraries is being used with success for applications such as backup and scientific data collection, where data access patterns are strictly sequential. In this paper, we evaluate striped performance for randomly distributed accesses to the tape library. We believe such operations will be characteristic of future tertiary storage databases using large objects, such as on-line libraries and multimedia databases. Using an event-driven simulator, we show that striped large tape libraries perform poorly for this random workload because striping causes contention for the small number of readers and robot arms in these libraries. Increasing the number of readers results in better striped performance. We also examine how the effectiveness of striping ...