Abstract
Compared with the traditional hard-disk drives (HDDs), solid-state drives (SSDs) have adopted NAND flash memory and become the current popular storage devices. However, when the free space in NAND flash memory is not enough, the garbage collection will be triggered to recycle the free space. The activities of the garbage collection include a large amount of data written and time-consuming erase operations that can reduce the performance of NAND flash memory. Therefore, DRAM is usually added to NAND flash memory as cache to store frequently used data. The typical cache methods mainly utilize the data characteristics of temporal locality and spatial locality to keep the frequently used data in the cache as much as possible. In addition, we find that there are not only temporal/spatial locality, but also certain associations between the accessed data. Therefore, we suggest that a cache policy should not only consider the temporal/spatial locality but also consider the association relationship between the accessed data to improve the cache hit ratio. In the paper, we will propose a cache policy based on request association analysis for reliable NAND-based storage systems. According to the experimental results, the cache hit ratio of the proposed method can be increased significantly when compared with the typical cache methods.
Highlights
Compared with the traditional hard-disk drives (HDDs), solid-state drives (SSDs) adopt NAND flash memory as the storage medium that has the advantages of non-volatility, fast speed, shock resistance, low power consumption, and small size
We will propose a cache policy based on request association analysis for reliable NAND-based storage systems
For MSR-usr_0, Figure 10a shows that RAA makes 42.25%, 28.77% and 35.27% improvements of the average hit ratio when compared with LRU, adaptive replacement cache (ARC), and VBBMS, respectively
Summary
Compared with the traditional hard-disk drives (HDDs), solid-state drives (SSDs) adopt NAND flash memory as the storage medium that has the advantages of non-volatility, fast speed, shock resistance, low power consumption, and small size. When the number of free pages in NAND flash memory is not enough, the activities of garbage collection will first select a victim block, copy the victim block’s valid pages to other free pages and erase the victim block to generate a free block. The activities of garbage collection can reduce the performance of NAND flash memory. DRAM can be added to SSDs as a cache to store frequently used data because DRAM has a higher access speed and better reliability than NAND flash memory. When the limited cache space is full, it is still an important research topic to select the appropriate victims to be replaced
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