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Key Technology Researches For Hybrid Storage Systems Based On Phase Change Memory

Posted on:2017-04-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z L WuFull Text:PDF
GTID:1108330485451627Subject:Computer application technology
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Computer technology has been developed rapidly from the past several decades. Currently, computer systems consist of several processors, which allow different threads or applications to execute concurrently. The total data set of the system increases with the number of parallel programs increases, which in turn increases the demands of memory size and the data access performance. Meanwhile, in the information age, the data are generated explosively, the demands of efficiently handling and storing massive data in the computer system are also increases. To solve these problem, one way is enlarge the size of DRAM memory. Although it improves the data access performance significantly, the computer systems suffer from the problems of high cost and energy consumption. What’s more, extending the capacity of single nod DRAM memory is difficult. Using SSDs in the storage system can also shorten the latency of accessing data in some degree, but the feature of "erase before write" limits the I/O performance of SSDs, CPU still has to go through a long I/O process to finish one data access. In a word, traditional storage architecture still suffer from the performance bottleneck between DRAM memory and disk, which can’t meet the need of massive data accessing and storing. A new innovative storage architecture and data managing schemes are desiderated to greatly enhance the performance of computer system.Phase change memory, as a new kind of storage medium, blurs the distinction between memory and secondary storages and the technical change in designing the computer storage systems. However, PCM also has disadvantages, such as read and write asymmetry, limited lifetime, long write latency, and so on. Therefore, PCM can not replace traditional DRAM memory completely. Instead, constructing the PCM-based hybrid storage system with DRAM memory is a more practical way.Studying the PCM-based hybrid storage system is a new research topic. This paper analyzes the existing research findings about PCM-based hybrid memory system and persistent storage system and points out the key problems in these research fields. Then, we launch the research work on PCM&DRAM based hybrid memory system and storage sub-system of PCM-based devices.The key technologies about PCM&DRAM based hybrid memory system consist of memory page replacement policy and free space management and allocation. Except for keeping the same design goal with traditional memory technologies, these PCM-based memory technologies should also take measures to lengthen the lifetime of PCM.Improving the hit ratio is the main goal in the design of traditional page replacement policies, which directly influences the total performance of system. But in hybrid memory system, the design goal of page management policy includes two aspects, one is maintaining the hit ratio, the other one is reducing writes to PCM. In this paper, we carry out the studies on the memory management of hybrid memory system. which include page replacement, partition, migration, and so on. These memory managements predict the page’s access tendency by historical read or write information, or introduce recent rewrite distance and write recency to determine and evaluate the write hotness of pages. Meanwhile, we also predict pages’access patterns when they are loaded to memory and allocate appropriate free pages for them.This paper also does research on free space management and allocation about PCM based memory systems. Firstly, we analysis the potential performance affection on computer system of wear leveling algorithms on PCM-based memory and lifetime deterioration when using traditional free pages management algorithm on PCM. Then, a novel free memory pages management and allocation algorithm is propose, which utilizes the idea of min-heap to manages free spaces and combines free memory space allocation with page-level wear leveling. The proposed policy can not only guarantee the effectiveness of space allocation but also achieve page-level wear leveling without extra page swapping.PCM can also be expected to become a new emerging persistent storage devices. Under this background, this paper also discusses the space management for PCM based storage devices. We design a wearing based page classification method, and cooperate the neoteric buffer management method with PCM free pages allocation and data migration mechanism to prolong the lifespan of PCM.The main contributions of this paper are as follows.(1) We present a historical access information aware buffer managing algorithm for PCM&DRAM based hybrid memory systems. First, this algorithm evaluates and predicts pages’read/write tendency by historical read or write information. And then, it designs an efficient page allocation and data migration policy to reduce the total writes on PCM.(2) Base on the PCM&DRAM hybrid memory systems, we propose a memory page managing policy, which introduces recent rewrite distance and write recency to predict the write hotness of pages. The policy utilizes a write clock list to track the change of pages’ write hotness over time, to achieve dynamic monitoring of access patterns and migration of pages.(3) Aiming at PCM memory, we propose free memory space management and allocation method. The method designs a data structure called min-heap array to manage the free memory space, and allocates free pages on account of PCM wear leveling. This can avoid write amplification incurred by page swapping, which is the most common way in existing wear leveling algorithms.(4) For a PCM device with a DRAM buffer, we propose a novel space managing policy, which manages and groups pages using two dynamic bucket lists. What’s more, in the subsystem of PCM device, the delayed caching mechanism in buffer management and wear-leveling aware PCM space management are working together to achieve the final goal of lengthen the lifetime of PCM.
Keywords/Search Tags:phase change memory, hybrid storage system, page replacement, space management, page allocation, data partition, data migration
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