In recent years, increased I/O demand of Virtual Machines (VMs) in large-scale data centers and cloud computing has encouraged system architects to design high-performance storage systems. One common approach to improving performance is to employ fast storage devices such as Solid-State Drives (SSDs) as an I/O caching layer for slower storage devices. SSDs provide high performance, especially on random requests, but they also have limited endurance: they support only a limited number of write operations and can therefore wear out relatively fast due to write operations. In addition to the write requests generated by the applications, each read miss in the SSD cache is served at the cost of imposing a write operation to the SSD (to copy the data block into the cache), resulting in an even larger number of writes into the SSD. Previous I/O caching schemes on virtualized platforms only partially mitigate the endurance limitations of SSD-based I/O caches; they mainly focus on assigning efficient cache write policies and cache space to the VMs. Moreover, existing cache space allocation schemes have inefficiencies: they do not take into account the impact of cache write policy in reuse distance calculation of the running workloads and hence, reserve cache blocks for accesses that would not be served by cache. In this article, we propose an Efficient Two-Level I/O Caching Architecture (ETICA) for virtualized platforms that can significantly improve I/O latency, endurance, and cost (in terms of cache size) while preserving the reliability of write-pending data blocks. As opposed to previous one-level I/O caching schemes in virtualized platforms, our proposed architecture 1) provides two levels of cache by employing both Dynamic Random-Access Memory (DRAM) and SSD in the I/O caching layer of virtualized platforms and 2) effectively partitions the cache space between running VMs to achieve maximum performance and minimum cache size. To manage the two-level cache, unlike the previous reuse distance calculation schemes such as Useful Reuse Distance (URD), which only consider the request type and neglect the impact of cache write policy , we propose a new metric, Policy Optimized reuse Distance (POD). The key idea of POD is to effectively calculate the reuse distance and estimate the amount of two-level DRAM+SSD cache space to allocate by considering both 1) the request type and 2) the cache write policy. Doing so results in enhanced performance and reduced cache size due to the allocation of cache blocks only for the requests that would be served by the I/O cache. ETICA maintains the reliability of write-pending data blocks and improves performance by 1) assigning an effective and fixed write policy at each level of the I/O cache hierarchy and 2) employing effective promotion and eviction methods between cache levels. Our extensive experiments conducted with a real implementation of the proposed two-level storage caching architecture show that ETICA provides 45 percent higher performance, compared to the state-of-the-art caching schemes in virtualized platforms, while improving both cache size and SSD endurance by 51.7 and 33.8 percent, respectively.

中文翻译：

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ETICA： E高效的 Ť级别 一世/ O C疼痛 一种虚拟平台的架构

近年来，I / O需求增加 虚拟机大型数据中心和云计算中的虚拟机（VM）鼓励系统架构师设计高性能存储系统。提高性能的一种常见方法是采用快速存储设备，例如固态硬盘（SSD）作为I / O缓存层，用于速度较慢的存储设备。SSD可以提供高性能，尤其是在随机请求时，但它们的耐用性也很有限：它们支持只要 数量有限的写操作，因此可以 磨损由于写操作相对较快。除了由应用程序生成的写请求之外，SSD缓存中的每个读取未命中都会以对SSD进行写操作（将数据块复制到缓存中）为代价，从而导致更大数量的写操作放入SSD。虚拟平台上的以前的I / O缓存方案只要部分缓解基于SSD的I / O缓存的持久性限制；它们主要致力于为VM分配有效的缓存写入策略和缓存空间。此外，现有的缓存空间分配方案效率低下：不要 考虑到缓存写入策略对正在运行的工作负载的重用距离计算的影响，因此，将缓存块预留给将要访问的访问 不是由缓存提供。在本文中，我们建议E高效的 Ť级别 一世/ O C疼痛 一种建筑结构（ETICA）用于虚拟化平台，可以显着改善I / O延迟，耐用性和成本（就缓存大小而言），同时保留待写数据块的可靠性。与以前相反一级 虚拟平台中的I / O缓存方案，我们建议的体系结构1）提供 二 通过同时使用两个级别的缓存 动态随机存取存储器虚拟化平台的I / O缓存层中的（DRAM）和SSD（2）有效地在运行的VM之间划分缓存空间，以实现最高性能和最小缓存大小。管理二级缓存，与以前的重用距离计算方案不同，例如有用的再利用距离 （URD），它仅考虑请求类型，而忽略了 缓存写入策略 ，我们提出了一个新的指标， 策略优化的重用距离（荚）。POD的关键思想是通过同时考虑1）请求类型和2）缓存写策略来有效地计算重用距离并估计要分配的两级DRAM + SSD缓存空间的数量。由于分配了高速缓存块，这样做可以提高性能并减小高速缓存大小只要I / O缓存将服务的请求。ETICA通过以下两种方式来保持待写数据块的可靠性，并通过以下方式提高性能：1）在I / O缓存层次结构的每个级别上分配有效和固定的写入策略，以及2）在缓存级别之间采用有效的升级和逐出方法。我们对提议的两级存储缓存体系结构的实际实现进行的广泛实验表明，与虚拟化平台中的最新缓存方案相比，ETICA提供了高出45％的性能，同时提高了缓存大小和SSD耐久性分别增长51.7％和33.8％。