On demand of various applications for storage virtualization, this paper presents a stackable block-level virtual snapshot device (VSD) based on the virtual storage pool. With the strategy of stackable block device, VSD employs a read-only snapshot model with serial connection, and a tree model mixed with serial and parallel connection for writable snapshot. Moreover, two data updating schemes, Copy on Write and Realloc on Write, are integrated into VSD. Thus, VSD supports various applications such as data backup and recovery, data version management and volume clone and so on. Finally, the storage requirements and I/O performance of VSD are evaluated.
To achieve theoretical optimum of spatial locality based replacement algorithms, this paper proposes a Block Correlations Directed cache replacement policy (BCD) which uses both of history and runtime access information to predict spatial locality, designs a replacement policy to use prediction results to improve the utilization of the cache and reduces the penalty incurred by incorrect predications. For most of real system workloads, BCD can reduce the cache miss ratio by 11%~38% compared with LRU and the miss ratio is only high than the theoretical optimum by 0%-7.9%.
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