Research And Implementation On Read Only Raid And Tape Library System

As a robust storage medium, magnetic tape is used widely in geological exploration. Along with the development of data acquisition, transmitting and processing technologies, greater demand will be set on its reading and searching ability. However, magnetic tape is a sequence access device and has poor performance in random access. Improving its random access performance is therefore crucial for the design of magnetic tape library storage system. This dissertation introduces a Read only RAID and Tape library storage system using disk as the cache of tape, and makes further studies on improving its random access performance. The main contents of this dissertation are as follows:According to properties of the interface and data storing in geological exploration, a storage system based on Virtual Tape Library was proposed. The crucial components of this system include SCSI Target, disk-tape cache replacement algorithm and random I/O schedule algorithm for tape.The theoretical analysis and study on SCSI Target model were taken and a SCSI Target was implemented. On the basis of theoretical calculation and actual testing results, parameters of the SCSI target were determined. Furthermore, theoretical basis for the performance optimization was provided.A cache model for this storage system was built, and deep analyses and comparisons were made. Several influential factors in cache performance were presented. In the view of cache replacement mechanism, a cache replacement algorithm for this system was proposed. As some parameters of this algorithm required tuning, some tests on equipments were taken and the optimal parameters were determined on the basis of the testing results.According to the characteristics of magnetic tape in random I/O access, a random I/O schedule algorithm was proposed to improve the performance. On the basis of comparing several kinds of random schedule algorithms and the characteristics of data storing, a random schedule algorithm was proposed. This algorithm not only sorts the schedule queue, but also improves the merging process. Experiments and comparisons on real tape library were carried out to prove the correctness of this algorithm.The Read only RAID and Tape library system was implemented to verify the designed functions, compatibility, transmitting performance and random access performance.