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Summary: Solid state drives (SSDs) built upon MLC NAND flash memories suffer from a low lifetime endurance induced by continuously scaling‐down feature sizes and increasing bit density per cell. To cost‐effectively address this problem, we propose to integrate both hierarchical data redundancy and heterogeneous flash memory techniques into the SSD, named H2‐SSD. Through deploying across‐chips data redundancy in addition to conventional in‐page error correction codes, error correction capacity, so does the lifetime endurance of H2‐SSD can be dramatically improved. Furthermore, an extra small‐size sisngle‐level cell (SLC) chip is integrated into H2‐SSD to store across‐chips parities. Due to the high program/erase performance and lifetime endurance of that SLC chip, I/O performance degradation induced by the hierarchical data redundancy can be significantly mitigated, even under strict synchronous parity update strategies. Quantitative analysis and trace‐driven simulations are conducted to evaluate the effectiveness and efficiency of H2‐SSD, in both the scenes with and without degraded reads. Experimental results demonstrate that H2‐SSD outperform the conventional SSD in maximum Program/Erase cycles by 23% to 178%, and suffer from negligible degradation of I/O performance in terms of both throughput and average response time in most cases. [ABSTRACT FROM AUTHOR]

Summary: An effective way to mitigate the lifetime and performance problems of NAND flash SSDs induced by garbage collection is separating the cold data and hot data. However, all existing solutions do this separation from the viewpoint of the hot data and thus suffer from expensive cost on monitoring the update behaviors of workloads. Different from the conventional wisdom, we propose to do the separation from the viewpoint of the cold data, which is rooted on the following two dedicated observations. First, the data migrated by garbage collection demonstrate a cold property compared with the other data. Second, it is inexpensive to separate the former data from the latter data. In the proposed method, named Isolation, we inexpensively separate the cold data via garbage collection. More specifically, through writing the data migrated by garbage collection (cold data) to dedicated blocks and writing the other data (hot data) to other blocks, the separation is done naturally. To evaluate Isolation, we conduct extensive trace‐driven simulations under seven typical workloads. The simulation results demonstrate the effectiveness and efficiency of Isolation. In most cases, Isolation can reduce the number of erasures and average I/O response time up to 47.3% and 80.1%, respectively. Existing approaches integrated with Isolation can further reduce the number of erasures and average I/O response time up to 7.8%‐18.5% and 10.7%‐41.4%, respectively. [ABSTRACT FROM AUTHOR]

I/O performance has been critical for large-scale distributed systems. Many approaches, including hint-based multilevel cache, have been proposed to smooth the gap between different levels. These solutions demote or promote cache blocks based on the latest history information, which is insufficient for applications where frequent demote and promote operations occur. In this paper, we propose a novel multilevel buffer cache using K-step hints (Hint-K) to improve the I/O performance of distributed systems. The basic idea is to promote a block from the lower level cache to the higher level(s) or demote a block vice versa based on the block's previous K-step promote or demote operations, which are referred to as K-step hints. If we make an analogy between Hint-K and LRU-K, then LRU-K keeps track of the times of last K references for blocks within a single cache level, while our Hint-K keeps track of the information of the last K movements (either demote or promote) of blocks among different cache levels. We develop our Hint-K algorithms and design a mathematical model that can efficiently describe the activeness of any block in any cache level. Simulation results show that Hint-K achieves better performance compared to the existing popular multilevel cache schemes such as PROMOTE, DEMOTE, and MQ under different I/O workloads. [ABSTRACT FROM AUTHOR]