连续数据存储中面向RAID5的写操作优化设计

针对连续数据存储应用,如视频监控、连续数据保护(CDP)、虚拟磁带库(VTL)等,提出一种面向RAID5的写操作优化方法：首先进行基于区间映射(area mapping)的地址转换(AT),把非连续的I/O请求虚拟地址转换为连续的物理地址,以实现对磁盘阵列的连续写;然后,在缓冲区内保存应用程序发出的写数据块,并构造一个与RAID5的完整条带长度相等的对齐数据块,对齐数据块在RAID5上恰好占满整个条带,再发送给RAID5,以实现对RAID5的完全写.这样写入的数据块恰好占满RAID5的整个条带,不仅避免了因生成校验数据而产生重构写、读改写等额外I/O开销,而且数据块的连续写入有效降低了磁头的寻道时间,提高了RAID5的吞吐能力.实验表明,该写优化方法在有限降低RAID5读性能的同时,可大幅提高RAID5的写性能,在80%连续的负载下,使RAID5的数据传输率接近其最大值.在连续数据存储中该方法同样适用于RAID4和RAID6.     

一种适用于分布式存储集群的纠删码数据更新方法

目前分布式存储集群广泛采用纠删码来保证数据可靠性,但是数据更新密集时存储集群的磁盘I/O开销会成为性能瓶颈.在常用的纠删码数据更新方法中,磁盘I/O开销主要包括：1)更新数据块时对数据节点的读后写操作;2)更新校验块时读写日志的磁盘寻道开销.针对这些问题,提出PARD(parity logging with reserved space and data delta)数据更新方法,其主要思想是首先利用纠删码线性运算的特性来减少读后写操作;然后根据磁盘特性来降低磁盘寻道开销.PARD包含3个设计要点：1)采用即时的数据块更新和基于日志的校验块更新;2)利用纠删码线性运算的特性,构建基于数据增量的日志,极大限度地消除对数据节点的读后写操作;3)根据磁盘特性,在数据文件末尾为日志预留空间,减少读写日志的磁盘寻道开销.实验结果表明,当块大小为4 MB时,PARD的更新吞吐率相较于PLR(parity logging with reserved space),PARIX(speculative partial write),FO(full overwrite),分别至少提升了30.4%,47.0%,82.0%.     

一种基于RAID5的Disk Cache的实现

介绍了一种基于RAID5的Disk Cache的实现。在对磁盘阵列Cache的实现过程中,使用了组相联映射、LRU替换算法等比较成熟的技术,在Cache回写策略上采用write-back方式。从而提高了写磁盘速度,减少冗余写盘操作。另外通过对校验组加锁,有效地防止了同一校验组里多个块同时降级而导致的数据不一致现象。     

基于磁盘异或引擎的RAID-5小写性能优化

SCSI标准中已扩充了新的SCSI命令(XDWRITE，XDREAD，XPWRITE等)，用以实现高效RAID-5写操作。对“小写”操作，传统的方法需要主机或RAID控制器读入原有的校验块，通过异或计算来构造新的校验块。采用这些新的SCSI命令实现“小写”操作，不再需要读入校验块，由磁盘来进行异或运算构造出校验块。利用磁盘的异或引擎，提高了RAID-5的吞吐率，缩短了平均响应时间。     

一种新型的能够防止两块磁盘失败的技术

海量存储系统的建设是目前计算机系统最热门和发展最快的领域,存储系统的主要部分是在线存储系统。RAID(磁盘阵列)对于提升存储系统的效率、数据的高可靠性、防止数据破坏和业务停顿具有重大意义。目前实际应用中的RAID 1,RAID 0+1,RAID 4,RAID 5都只能防止单块磁盘的损坏,实际生产中已经出现了很多由于双盘损坏造成业务长时间停顿的事故。在介绍了通用的RAID级别的基础上,介绍了一种新型的对角线奇偶校验方法,结合水平奇偶校验,可以防止两块磁盘损坏。通过可靠的数学分析,可以看到该方法可以极大提高磁     

自修复磁盘阵列技术研究

以数据为中心的计算模式对数据的可靠性提出新的需求,高可靠存储设备成为高性能计算的基础.自从Xiotech公司提出ISE结构并取得成功后,关注磁盘失效之前的征兆而不是失效后的具体处理的"自修复"概念已成为磁盘阵列设计新的指导思想之一.提出存储系统可靠性系数的概念,分析单个磁盘可靠性与磁盘阵列可靠性关系,选择合适的磁盘S.M.A.R.T属性结合磁盘当前利用率和历史信息建立评定磁盘状态的T~2US算法,接着介绍RAID 5结合T2US监测的高可靠、自修复的RAID 5T结构,说明RAID 5T结构的运行方式和磁盘不符合T~2US监测标准时数据迁移策略,最后对结构的可靠性利用存储系统可靠性系数和MTTF分别进行了分析.     

用户怎样重获存储控制权

Storage Computer公司将在其开放系统存储结构中增加新的容错等级,将存储权重新交回到管理者手中。两项新的应用名为OmniForce和OmniRAID,它们分別提供映射和可定制的RAID(廉价磁盘冗余阵列)组态。这两项技术的关键在于用户能够确定存储数据的去向以及所处的RAID等级。每个产品均适用于该公司的Storage Server和Storage SuperServer软件生产线,此生产线还包括公司专利产品RAID 7结构,RAID 7通过从4台热备份驱     

RAID如何选

所谓磁盘阵列,就是利用多个硬磁盘,来提高存取速度、将磁盘故障时的危害降低到最低限度的机构。磁盘阵列也叫 RAID,原本是在大型计算机中,使用多个廉价小型(5.25或3.5 inch)磁盘来扩大磁盘容量的。RAID 根据数据的分散方法和冗余数据的生成/记录方法,定义成0～5级6种。现在,主要使用的是RAID0、1、3、5(见表).RAID0是一种以块为单位将数据分散记录在多个磁盘上,也叫磁盘分条。由于对于多个磁盘可以并行读写数据,所以比起一台磁盘来,读/写性能都得到了显著提高。但用 RAID0不能提高抗故障能力。譬如说,用2台磁盘构成 RAID0,数据分散记录在2台磁盘上,但只要有一个磁盘发生故障,数据就全部丢掉     

大麻Marijuana病毒的诊断、激活和解毒程序

大麻病毒(也叫Marijuana病毒,或Stone病毒)是一种恶性的操作系统型病毒,病毒感染磁盘后,篡改了磁盘原有的引导记录,并将原有的引导记录移到磁盘的其它位置上。病毒被激发后,屏幕左上角出现:Your PC is now Stoned!……LEGALISE MARIJU-AHA!,同时响铃。大麻病毒的危害取决于病毒将磁盘原来的引导记录移到磁盘的什么位置上:对软盘来说,病毒将原来的引导记录从0磁道0磁头1扇区移到0磁道1磁头3扇区,常用的1.2M的双面高密度软盘和360K的双面双密度软盘的0磁道1磁头3扇区在磁盘的目录区中,存储在这个扇区中的32个目录项就被破坏了;对硬盘来说,病毒将原来的主引导记录(分区表)从0磁道0磁头1扇区移到0磁道0磁头7扇区,病毒对硬     

一种高性能高可靠的混合客户端缓存系统

现代数据中心普遍使用网络存储系统提供共享存储服务.存储服务端通常使用独立冗余磁盘阵列(RAID)技术保障数据可靠性,如可以容单/双盘错的RAID5/6.相比于传统磁盘,固态盘具有更低的访问时延和更高的价格,因此将固态盘作为存储客户端缓存成为一种流行的方案.写回法可以充分发挥固态盘的优势加速存储读写性能,然而一旦固态盘发生故障,写回法无法保证数据的一致性和持久性.写直达法简化了一致性模型,但是无法减小写时延.设计并实现一种新的混合客户端缓存(hybrid host cache, HHC),HHC通过使用廉价的日志磁盘镜像存放固态盘上的脏数据来提高可靠性,并且利用写屏障语义保证数据的可靠性和一致性.分析表明,HHC的平均无故障时间远远高于后端存储系统.最后实现了一个原型系统并使用Filebench进行性能评估,结果表明在不同负载下,HHC性能与传统的写回法接近,远远超过写直达法.     

高密度磁记录技术研究综述

大数据时代对大容量磁盘的需求日益增长,而在对现有的磁盘不进行较大改动的前提下,叠瓦式磁记录技术SMR是提高磁盘存储容量的最佳选择.近年来,兴起了一种新的磁记录技术——交错式磁记录技术IMR,它可以获得比SMR更高的存储密度和随机写性能.首先介绍了SMR磁盘的内部叠瓦式结构以及由此带来的数据写放大问题,并对缓解数据写放大问题的数据管理方式、性能特性评测以及基于SMR的上层应用系统方面的研究进展进行了概述;然后对新兴的IMR磁盘内部结构及其数据写放大问题进行了介绍,并对其将来的研究方向做了一定的分析和展望;最后对SMR磁盘和IMR磁盘在存储密度、数据写性能等方面进行了比较分析.当前有很多基于SMR磁盘的上层应用系统,这表明SMR磁盘可以高效地替代传统磁盘来构建大型的存储系统,而IMR磁盘的优势也将使其未来的发展前景可期.     

Reconstruct versus read-modify writes in RAID

RAID5 (Redundant Arrays of Independent Disk level 5) is a popular paradigm, which uses parity to protect against single disk failures. A major shortcoming of RAID5 is the small write penalty, i.e., the cost of updating parity when a data block is modified. Read-modify writes and reconstruct writes are alternative methods for updating small data and parity blocks. We use a queuing formulation to determine conditions under which one method outperforms the other. Our analysis shows that in the case of RAID6 and more generally disk arrays with k check disks tolerating k disk failures, RCW outperforms RMW for higher values of N and G. We note that clustered RAID and variable scope of parity protection methods favor reconstruct writes. A dynamic scheme to determine the more desirable policy based on the availability of appropriate cached blocks is proposed.     

RAID 4SMR: RAID Array with Shingled Magnetic Recording Disk for Mass Storage Systems

One way to increase storage density is using a shingled magnetic recording (SMR) disk. We propose a novel use of SMR disks with RAID (redundant array of independent disks) arrays, specifically building upon and compared with a basic RAID 4 arrangement. The proposed scheme (called RAID 4SMR) has the potential to improve the performance of a traditional RAID 4 array with SMR disks. Our evaluation shows that compared with the standard RAID 4, when using update in-place in RAID arrays, RAID 4SMR with garbage collection not just can allow the adoption of SMR disks with a reduced performance penalty, but offers a performance improvement of up to 56%.

     

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.     

利用DCMT来解决RAID5的小写问题

在盘阵中，RAID5利用校验信息来提高数据的可靠性。由于要维护校验信息，带来了小写问题，影响了系统的整体性能。本文在AFRAID方法的基础上，提出了一种基于动态缓存标志表（DCMT）的提高RAID5性能的方法。该方法在保证RAID5磁盘数据特征的前提下，用较小的代价就可以大大缩短响应时间，提高系统整体性能。     

Cascaded Write Amplification of LSM-tree-based Key-Value Stores underlying Solid-State Disks

Log-structured merge tree (i.e., LSM-tree)-based key–value stores (i.e., KV stores) are widely used in big-data applications and provide high performance. NAND Flash-based Solid-state disks (i.e., SSDs) have become a popular storage device alternative to hard disk drives (i.e., HDDs) because of their high performance and low power consumption. LSM-tree KV stores with SSDs are deployed in large-scale storage systems, which aims to achieve high performance in the cloud. Write amplification in LSM-tree KV stores and NAND Flash memory in SSDs are defined as WA1 and WA2 in this paper. The former, which is attributed to compaction operations in LSM-tree-based KV stores, is a burden on I/O bandwidth between the host and the device. The latter, which results from out-place updates in NAND Flash memory, blocks user I/O requests between the host and NAND Flash memory, thereby degrading the SSD performance. Write amplification impairs the overall system performance. In this study, we explored the two-level cascaded write amplification in LSM-tree KV stores with SSDs. The cascaded write amplification is represented as WA. Our primary goal is to comprehensively study two-level cascaded write amplification on the host-side LSM-tree KV stores and the device-side SSDs. We quantitatively analyze the impact of two-level write amplification on overall performance. The cascaded write amplification is 16.44 (WA1 is 16.55; WA2 is 0.99) and 35.51 (WA1 is 16.6; WA2 is 2.14) for SSD-I and SSD-S with LevelDB’s default setting under DB_bench. The larger cascaded write amplification of KV stores has a bad impact on SSD performance and lifetime. The throughput of SSD-S and SSD-I under an 80%-write workload is approximately 0.28x and 0.31x of that under a 100%-write workload. Therefore, it is important to design a novel approach to balance the cost of an SSD lifetime caused by cascaded write amplification and its high performance under the read-write-mixed workloads. We attempt to reveal details of cascaded write amplification and hope that this study is useful for developers of LSM-tree-based KV stores and SSD software stacks.     

磁盘阵列校验信息的放置策略

廉价磁盘冗余阵列（ＲＡＩＤ）采用许多小的廉价磁盘来代替大容量昂贵的磁盘，以取得更高的性能和更低的功耗。本文介绍了ＲＡＩＤ－５级磁盘阵列中校验信息的八种不同的分布策略，即奇偶校验信息的放置策略，并从几个不同的应用情况对不同的放置策略进行了研究，结论是不同的奇偶校验信息放置策略对磁盘阵列的Ｉ／Ｏ读写性能有很大的影响。