The Real Effect of I / O Optimizations and Disk Improvements
The Real Effect of I / O Optimizations and Disk Improvements
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I/O 优化和磁盘改进的实际效果
DOI：
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发表时间：
2003
期刊：
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通讯作者：
A. Smith
中科院分区：
文献类型：
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作者：
W. Hsu;A. Smith
人们发明了许多优化技术来掩盖存储设备（最重要的是磁盘）缓慢的机械特性。然而，关于这些技术对真实的工作量的有效性的数据要么缺乏，要么没有可比性。磁盘技术也在多个方面稳步改进，但很难将各种物理改进与真实的工作负载所经历的实际性能联系起来。在本文中，我们使用各种各样的真实的服务器和个人计算机的工作负载，系统地分析各种优化技术和技术改进，以确定其真正的性能影响。我们研究的技术包括读缓存，顺序预取，机会预取，写缓冲，请求调度，条带化和短行程。我们还将磁盘技术的稳步改进分解为四个主要的基本效果-更快的寻道速度，更高的RPM，线性密度的改善和磁道密度的增加-并分别分析每一个以确定其实际好处。此外，我们还检查了历史改进率，并使用趋势来预测磁盘技术扩展的效果。作为本研究的一部分，我们开发了一种方法来重放真实的工作负载，更准确地模拟I/O到达的时间，并允许I/O速率比以前的做法更现实的规模。我们的研究结果表明，顺序预取和写缓冲是两个最有效的技术，提高性能，减少平均读取和写入响应时间分别约50%和90%。对于我们的工作量，改善机制本研究的资金已提供由加州的MICRO计划下，并由AT&T实验室，思科公司，富士通微电子，IBM，英特尔公司，迈拓公司，微软公司，太阳微系统公司，东芝公司和Veritas软件公司。磁盘的cal组件每年将平均响应时间缩短8%。这种改进主要是由于转速的增加而不是寻道时间的减少。此外，我们发现，在磁盘的记录密度的增加可以实现一个同样可观的改善真实的性能，与大部分的增益来自线性密度的改善，这增加了传输速率，而不是轨道密度缩放。对于给定的工作负载，如果磁盘占用率保持不变，则按历史速度发展的磁盘技术预计每年可将性能提高约8%。我们还观察到，磁盘将大部分时间用于定位磁头，而不是传输数据。我们认为，为了有效地利用可用的磁盘带宽，块应该以这样一种方式进行重组，即访问变得更加顺序。
Many optimization techniques have been invented to mask the slow mechanical nature of storage devices, most importantly disks. Data on the effectiveness of these techniques for real workloads, however, are either lacking or are not comparable. Disk technology has also improved steadily in multiple ways but it is difficult to relate the various physical improvements to the actual performance experienced by real workloads. In this paper, we use an assortment of real server and personal computer workloads to systematically analyze the various optimization techniques and technology improvements to determine their true performance impact. The techniques we study include read caching, sequential prefetching, opportunistic prefetching, write buffering, request scheduling, striping and short-stroking. We also break down the steady improvement in disk technology into four major basic effects – faster seeks, higher RPM, linear density improvement and increase in track density – and analyze each separately to determine its actual benefit. In addition, we examine the historical rates of improvement and use the trends to project the effect of disk technology scaling. As part of this study, we develop a methodology for replaying real workloads that more accurately models the timing of I/O arrivals and that allows the I/O rate to be more realistically scaled than previous practice. Our results show that sequential prefetching and write buffering are the two most effective techniques for improving performance, reducing the average read and write response time by about 50% and 90% respectively. For our workloads, improvement in the mechaniFunding for this research has been provided by the State of California under the MICRO program, and by AT&T Laboratories, Cisco Corporation, Fujitsu Microelectronics, IBM, Intel Corporation, Maxtor Corporation, Microsoft Corporation, Sun Microsystems, Toshiba Corporation and Veritas Software Corporation. cal components of the disk reduces the average response time by 8% per year. Most of this improvement results from increases in the rotational speed rather than reduction in the seek time. In addition, we discover that increases in the recording density of the disk can achieve an equally sizeable improvement in real performance, with most of the gain coming from linear density improvement, which increases the transfer rate, rather than track density scaling. For a given workload, disk technology evolution at the historical rates can be expected to increase performance by about 8% per year if the disk occupancy rate is kept constant. We also observe that the disk is spending most of its time positioning the head rather than transferring data. We believe that to effectively utilize the available disk bandwidth, blocks should be reorganized in such a way that accesses become more sequential.