一种基于闪存的混合存储仿真系统

近年来闪存发展非常迅速,已成为一种大容量、高性能、低功耗、非易失的新型存储产品,其可以有效弥补内存和磁盘的性能差距完善存储系统。为此,设计一种基于闪存的混合存储仿真系统HybridArch,增加文件分布层,支持文件的分割、分布和文件接口访问,并实现5种混合存储体系结构,包括传统的内存-磁盘双层结构、纯闪存结构、闪存作为部分磁盘结构、塔式结构和水平缓存结构。基于HybridArch对上述混合存储体系结构进行仿真实验,分析比较其在性能和闪存写入量等方面的优劣,结果表明,水平缓存体系结构在性能、性价比、闪存设备寿命等方面综合表现较好。     

利用页面重构与数据温度识别的闪存缓存算法

基于闪存的固态盘(SSD)具有比磁盘更加优越的性能,并且在桌面系统中逐渐替代磁盘。但是,尽管在SSD中嵌入了DRAM作为缓存,闪存在不断写入的过程中也可能产生不稳定的写性能,主要是因为逻辑页写入时会频繁引发非覆盖写和垃圾回收操作。针对此问题,提出了一种叫作PRLRU的新型闪存缓存管理方法,通过页面重构机制以及数据温度识别机制来管理缓存区。页面重构机制把即将回写的有效数据未满一个整页大小的页与多个其他有效数据不足一个页大小的页进行数据重组后再回写至闪存,通过尽可能减少非覆盖写操作来达到减少实际写操作的目的。数据温度识别机制通过对缓存页进行温度等级标记,按预定优先级顺序回写缓存页。对真实负载进行测试,实验结果表明,PRLRU能够有效提高SSD性能并延长SSD使用寿命,与LRU、BPLRU和2QW-Clock三种算法相比,写性能平均分别提高了34.5%、22.8%和28.8%,读性能平均分别提高了12.5%、10.6%和8.3%,垃圾回收数量平均分别降低了10.5%、8.7%和6.3%。     

一种基于闪存固态硬盘的辅助缓冲池设计

基于磁盘数据库系统的瓶颈主要在磁盘I／O,通常采用缓冲池的设计,将读到的数据页先放入到内存缓冲池后再进行操作。因此,缓存池的大小直接决定了数据库的性能。通过研究基于闪存固态硬盘的特性,提出了一种基于闪存固态硬盘的辅助缓冲池设计。最后,通过修改开源数据库MySQL InnoDB存储引擎,并通过TPC-C实验对比分析了启用辅助缓冲池后数据库的性能可有100％-320％的提高。     

固态硬盘混合存储数据库的数据分布优化算法

基于闪存的固态硬盘( SSD)可以有效提升联机事务处理( OLTP)数据库的性能,但由于目前SSD价格仍然较高,一般多与磁盘组成混合存储。为此,提出数据分布的自适应优化算法以及具体的优化策略。该算法能够自动适应应用的特征,通过观测判断各个数据元素的性能提升效率,从而在SSD和磁盘之间自动形成理想的数据分布。基于实际数据库系统的实验结果表明,该算法可适应各种SSD空间配置,使基于混合存储的OLTP数据性能得到有效提升。     

内存数据库在TPC-H负载下的处理器性能

Ailamaki等人1999年研究了数据库管理系统(database management system,简称DBMS)在处理器上的时间开销分解.此后,相关研究集中在分析DBMS在处理器上的瓶颈.但这些研究工作均是在磁盘数据库DRDBs(disk resident databases)上开展的,而且都是分析DBMS上的TPC-C类负载.然而,随着硬件技术的进步,现代计算机的多级缓存结构(memory hierarchy)在逐渐地"上移".例如,容量越来越大的芯片内缓存(on-chip caches)和芯片外缓存(off-chip caches),容量越来越大的RAM,Flash Memory等等.为此,处理器负载分析的研究工作也应随之"上移".研究内存数据MMDBs(mainmemory resident databases)在计算密集型负载下的处理器行为特性.由于磁盘数据库的主要性能瓶颈是磁盘I/O,因而可以用索引、压缩等技术进行优化;然而,内存数据库的性能瓶颈却在于处理器和内存之间的数据交换.针对这一问题,首先分析了磁盘数据库和内存数据库在TPC-H负载下处理器性能瓶颈的差异,并给出了一些优化建议,提出了通过预取的优化方法.其次,通过实验比较了不同存储体系结构(行存储与列存储)对处理器利用率的差异,并探索了下一代内存数据库体系结构方面的解决方案.此外,还研究了索引结构对处理器多级缓存的影响,并给出了索引的优化建议.最后,提出一个微测试集用于评估内存数据库在DSS(decision support system)负载下处理器的性能及行为特性.研究结果会对运行于下一代处理器上的内存数据库体系结构设计和性能优化提供一定的实验依据.     

FClock:一种面向SSD的自适应缓冲区管理算法

现有的各种基于闪存的缓冲区管理算法针对闪存读写代价的不对称性进行改进,实际中既存在同一闪存读写代价的不对称性问题,也存在不同闪存不对称性之间的巨大差异性问题,而后者一直没有得到足够的重视.文章提出一种基于闪存硬盘(SSD)的自适应缓冲区管理算法FClock,FClock将数据页组织为两个环形数据结构(CC和DC),分别用于存储缓冲区中的只读数据页和已修改数据页.当需要选择置换页时,FClock使用基于代价的启发式来选择置换页,可在未修改的数据页和已修改的数据页之间进行公平的选择,适用于不同种类的SSD.针对数据库、虚存和文件系统中数据页访问存在高相关性的特点,提出基于"平均命中距离"的访问计数方法来调整数据页的访问频率.基于不同SSD和不同存取模式的实验结果说明,FClock的综合性能优于已有方法.     

内存网格中的自主协同缓存技术研究

本文基于原有工作提出了利用内存网格进行磁盘缓存的技术,从而组织和共享网络上分布的空闲内存资源,提高具有大量磁盘IO的节点的系统性能;给出了一种基本设计方案,并提出了缓存节点的时间分布和空间合并等自主协同机制,进一步优化了系统性能;最后通过基于实际采集数据的模拟,对方案进行了评价。     

HF-Tree:一种闪存数据库的高更新性能索引结构

随着电子技术的发展,闪存作为一种新型的电子存储设备具有高速的访问速度和无机械延迟的特性.但是由于闪存高昂的写操作代价,传统的基于磁盘的索引结构如果直接应用在闪存上会导致极差的更新性能.提出一种新颖的索引结构HF-Tree,通过组提交、更新合并以及多级延迟的方式来提高更新性能.HF-Tree能够有效地克服闪存和现有基于磁盘索引之间的不匹配性的问题.通过和经典的BFTL及IPL索引的性能比较,实验结果充分显示了HF-Tree优越的更新和查询性能.此外HF-Tree能够有效地减少擦除次数,从而延长闪存的使用寿命.     

磁盘驱动程序预写

较好地利用内存作为缓存，并优化磁盘设备的请求处理，是缓解系统I／O瓶颈的有效途径。提出一种驱动程序预写的方法来处理内存缓存中脏数据写回磁盘的方法，其基本思想是：通过将文件系统高速缓存中的脏数据写盘操作由磁盘设备驱动程序发起，磁盘可以在恰当的时间（设备空闲）或者恰当的位置（减少寻遣和设备旋转）完成写请求，减少缓存flush操作对当前应用的影响。模拟试验表明，谊方法能提高磁盘写操作的效率、系统数据的可靠性和系统的I／O性能。     

闪存数据库顺序和随机操作性能深度测试和分析

闪存作为一种可供替代磁盘的新型存储介质,已经开始越来越广泛地被个人和企业使用。固态硬盘(SSD)的速度大大超出磁盘,但因为数据库系统并未完全发挥闪存的特性,闪存数据库的性能并没有得到相应的提升。详细测试和研究SSD的顺序和随机操作的差异,进一步证明现代SSD具有较快的随机访问速度。选取具有代表性的数据库基准,调整各查询的查询计划,观察不同查询计划下数据库系统的性能。由此发现,某些查询计划可以更好地发挥出SSD的随机访问特性,其中某个查询的最佳性能甚至比使用默认的查询计划快6倍以上。最后,总结传统数据库系统面对SSD这一介质的短板,并提出一些优化的建议。     

A hybrid flash translation layer design for SLC-MLC flash memory based multibank solid state disk

This paper presents the design of a NAND flash based solid state disk (SSD), which can support various storage access patterns commonly observed in a PC environment. It is based on a hybrid model of high-performance SLC (single-level cell) NAND and low cost MLC (multi-level cell) NAND flash memories. Typically, SLC NAND has a higher transfer rate and greater cell endurance than MLC NAND flash memory. MLC NAND, on the other hand, benefits from lower price and higher capacity. In order to achieve higher performance than traditional SSDs, an interleaving technique that places NAND flash chips in parallel is essential. However, using the traditional FTL (flash translation layer) on an SSD with only MLC NAND chips is inefficient because the size of a logical block becomes large as the mapping address unit grows. In this paper, we proposed a HFTL (hybrid flash translation layer) which makes use of chained-blocks, combining SLC NAND and MLC NAND flash memories in parallel. Experimental results show that for most of the traces studied, the HFTL in an SSD configuration composed of 80% MLC NAND and 20% SLC NAND memories can improve performance compared to other solid state disk configurations, composed of either SLC NAND or MLC NAND flash memory alone.     

HAT: an efficient buffer management method for flash-based hybrid storage systems

Flash solid-state drives (SSDs) provide much faster access to data compared with traditional hard disk drives (HDDs). The current price and performance of SSD suggest it can be adopted as a data buffer between main memory and HDD, and buffer management policy in such hybrid systems has attracted more and more interest from research community recently. In this paper, we propose a novel approach to manage the buffer in flash-based hybrid storage systems, named hotness aware hit (HAT). HAT exploits a page reference queue to record the access history as well as the status of accessed pages, i.e., hot, warm, and cold. Additionally, the page reference queue is further split into hot and warm regions which correspond to the memory and flash in general. The HAT approach updates the page status and deals with the page migration in the memory hierarchy according to the current page status and hit position in the page reference queue. Compared with the existing hybrid storage approaches, the proposed HAT can manage the memory and flash cache layers more effectively. Our empirical evaluation on benchmark traces demonstrates the superiority of the proposed strategy against the state-of-the-art competitors.     

PostgreSQL闪存缓冲区置换算法扩展与性能验证

针对闪存缓冲区置换算法的性能验证基本采用仿真模拟的现状,提出了一种基于PostgreSQL的有说服力的性能验证方法,重点讨论了在PostgreSQL上扩展闪存缓冲区置换算法的方法和实现技术,并以CFLRU(clean first least recently used)和CCFLRU(cold clean first least recently used)算法为例,给出了具体的扩展过程。然后以一块固态硬盘作为数据存储设备进行性能测试,测试结果证明了基于PostgreSQL的扩展方法在缓冲区置换算法性能验证上的有效性。     

一种有效的异构盘高能效缓存机制

固态盘具有低功耗、高性能、耐冲击等优势,硬盘具有高容量、低价格等优势.通过改进文件系统的结构,把固态盘和硬盘结合起来,固态盘作为硬盘的大容量缓存,组成一个我们称之为异构盘的异构系统,其性能接近于固态盘,价格却接近于硬盘.同时,在硬盘有足够空闲时长时,使之关闭以减少能耗.针对大容量缓存,我们采用了合适的树形搜索结构,提出...     

Exploiting flash memory characteristics to improve performance of RAIS storage systems

Redundant array of independent SSDs (RAIS) is generally based on the traditional RAID design and implementation. The random small write problem is a serious challenge of RAIS. Random small writes in parity-based RAIS systems generate significantly more pre-reads and writes which can degrade RAIS performance and shorten SSD lifetime. In order to overcome the well-known write-penalty problem in the parity-based RAID5 storage systems, several logging techniques such as Parity Logging and Data Logging have been put forward. However, these techniques are originally based on mechanical characteristics of the HDDs, which ignore the properties of the flash memory. In this article, we firstly propose RAISL, a flash-aware logging method that improves the small write performance of RAIS storage systems. RAISL writes new data instead of new data and pre-read data to the log SSD by making full use of the invalid pages on the SSD of RAIS. RAISL does not need to perform the pre-read operations so that the original characteristics of workloads are kept. Secondly, we propose AGCRL on the basis of RAISL to further boost performance. AGCRL combines RAISL with access characteristic to guide read and write cost regulation to improve the performance of RAIS storage systems. Our experiments demonstrate that the RAISL significantly improves write performance and AGCRL improves both of write performance and read performance. AGCRL on average outperforms RAIS5 and RAISL by 39.15% and 16.59% respectively.     

一种面向SSD-HDD混合存储的热区跟踪替换算法

固态驱动器(SSD)读写性能优越,但成本高,因此在实践中人们往往利用SSD和普通硬盘(HDD)构建混合存储系统以获取较高的性价比.在混合存储系统中,如何使更多的IO请求能够命中SSD是充分利用SSD性能的关键.针对多任务共享存储环境下集中访问和随机访问IO存取模式并存,且通常情况下IO工作流大部分请求相对集中于有限区域内的特点,本文提出一种基于热区跟踪(HZT)的缓存替换算法.HZT算法充分考虑了IO工作流的空间局部性和时间局部性,利用IO工作流的历史访问信息,跟踪当前热区,并为热区数据块赋予更高的驻留SSD的优先级,能够有效提高混合存储中SSD缓存的命中率.经测试,在典型多任务共享存储环境下HZT算法可以使SSD缓存的命中率比使用LRU(Least Recently Used)算法的系统提高12%.采用适当的预取策略,该算法的命中率与LRU算法相比可获得23%的提升.     

A high-performance and endurable SSD cache for parity-based RAID

Solid-state drives (SSDs) have been widely used as caching tier for disk-based RAID systems to speed up dataintensive applications. However, traditional cache schemes fail to effectively boost the parity-based RAID storage systems (e.g., RAID-5/6), which have poor random write performance due to the small-write problem. What’s worse, intensive cache writes can wear out the SSD quickly, which causes performance degradation and cost increment. In this article, we present the design and implementation of KDD, an efficient SSD-based caching system which Keeps Data and Deltas in SSD. When write requests hit in the cache, KDD dispatches the data to the RAID storage without updating the parity blocks to mitigate the small write penalty, and compactly stores the compressed deltas in SSD to reduce the cache write traffic while guaranteeing reliability in case of disk failures. In addition, KDD organizes the metadata partition on SSD as a circular log to make the cache persistent with low overhead.We evaluate the performance of KDD via both simulations and prototype implementations. Experimental results show that KDD effectively reduces the small write penalty while extending the lifetime of the SSD-based cache by up to 6.85 times.     

网络存储系统中低开销高性能的第二级缓存替换算法的研究

针对网络存储访问特性所带来的第二级缓存性能降低的问题,提出了一种高性能的第二级缓存替换算法。本算法采用顺序页面检测机制,能根据缓存页面顺序程度的不同做出替换选择,以减少缓存失效引起随机访问磁盘的次数,避免不必要的磁头寻道和旋转开销,从而改善整个存储系统的性能。实验结果表明,在多种缓存大小下,本文算法能显著降低有效响应时间,使网络存储系统达到更优的性能。     

Linked instruction caches for enhancing power efficiency of embedded systems

The power consumed by memory systems accounts for 45% of the total power consumed by an embedded system, and the power consumed during a memory access is 10 times higher than during a cache access. Thus, increasing the cache hit rate can effectively reduce the power consumption of the memory system and improve system performance. In this study, we increased the cache hit rate and reduced the cache-access power consumption by developing a new cache architecture known as a single linked cache (SLC) that stores frequently executed instructions. SLC has the features of low power consumption and low access delay, similar to a direct mapping cache, and a high cache hit rate similar to a two way-set associative cache by adding a new link field. In addition, we developed another design known as a multiple linked caches (MLC) to further reduce the power consumption during each cache access and avoid unnecessary cache accesses when the requested data is absent from the cache. In MLC, the linked cache is split into several small linked caches that store frequently executed instructions to reduce the power consumption during each access. To avoid unnecessary cache accesses when a requested instruction is not in the linked caches, the addresses of the frequently executed blocks are recorded in the branch target buffer (BTB). By consulting the BTB, a processor can access the memory to obtain the requested instruction directly if the instruction is not in the cache. In the simulation results, our method performed better than selective compression, traditional cache, and filter cache in terms of the cache hit rate, power consumption, and execution time.     

Endurable SSD-Based Read Cache for Improving the Performance of Selective Restore from Deduplication Systems

Deduplication 通常在两个企业存储系统和云存储被使用了。克服性能挑战为选择恢复 deduplication 系统的操作, solid-state-drive-based (即,基于 SSD ) 读的缓存能为由缓冲加快被部署流行动态地恢复内容。不幸地,经常的数据更改由古典缓存计划导致了(例如, LRU 和 LFU ) 显著地弄短 SSD 一生当在 SSD 减慢 I/O 进程时。处理这个问题,我们建议新解决方案砍缓存极大地由扩大比例象 I/O 性能一样改进 SSD 的 write 耐久性长期流行(砍) 在写进基于 SSD 的缓存的数据之中的数据。砍缓存保留很长时间在 SSD 缓存砍数据减少的时期缓存代替的数字。而且,它在 deduplication 集装箱阻止不得人心或不必要的数据被写进 SSD 缓存。我们在一个原型 deduplication 系统实现了砍缓存评估它的性能。我们的试验性的结果显示砍缓存弄短潜伏选择与仅仅 deduplicated 数据的 5.56% 能力以小基于 SSD 的缓存的成本由 37.3% 的一般水准恢复。重要地,砍缓存由 9.77 的一个因素改进 SSD 一生。砍缓存为一个成本效率的基于 SSD 的读的缓存解决方案提供到的证据表演增加性能选择为 deduplication 恢复系统。