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收集所有交通大學研究人員與學生個人或團體所發表之各項學術著作，涵蓋期刊論文、教師專書、學位論文等項。;;Collections of Publications of NCTU Researchers and Students Like Journal Papers and Thesis.

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Now showing 1 - 6 of 6

File Fragmentation in Mobile Devices: Measurement, Evaluation, and Treatment
(2019-09-01)
Ji, Cheng
;
Chang, Li-Pin
;
Hahn, Sangwook Shane
;
Lee, Sungjin
;
Pan, Riwei
Mobile devices, such as smartphones, have become a necessity in our daily life. However, users may notice that after being used for a long time, mobile devices begin to exhibit a sluggish response. Based on an empirical study on a collection of aged smartphones, this work identified that file fragmentation is among the key factors that contribute to the progressive degradation of response time. This study takes a three-step approach: First, this study designed a set of reproducible file-system aging processes based on User-Interface (UI) script replay. Through the aging processes, it confirmed that file fragmentation quickly emerged, and SQLite files were among the most severely fragmented files. Second, based on the workloads of a selection of popular mobile applications, this study observed that file fragmentation did have an impact on user-perceived latencies. Specifically, the launching time of Chrome on an aged file system was 79 percent slower than it was on a pristine file system. Third, this study evaluated existing treatments of file fragmentation, including space preallocation, persistent journal, and file defragmentation to understand their efficacies and limitations. This study also evaluated a state-of-the-art copyless defragmenter, janusd, to show its advantage over the existing methods.
Lightweight, Integrated Data Deduplication for Write Stress Reduction of Mobile Flash Storage
(2018-11-01)
Yen, Miao-Chiang
;
Chang, Shih-Yi
;
Chang, Li-Pin
;
資訊工程學系
;
Department of Computer Science
Recently, smartphone users are becoming reluctant to replace their devices, so providing reliable data storage throughout the increasingly long smartphone replacement cycle is an imminent challenge. We advocate an integrated approach to data deduplication, which involves the host I/O stack and the storage firmware, to reduce the write stress of mobile storage for lifespan extension. First, we identified that the SQLite library produces a large amount of copy-induced duplicate data, which can be fully revealed to the mobile storage through proper file format alignment. Second, inspired by the short flash read latency, we present a firmware-based method to efficiently identify duplicate data without any hardware support. Third, we enhance the flash garbage collector with the awareness of data deduplication. Based on a selection of popular mobile applications, our simulation results show that prior methods, which employ data compression or differential logging, are ineffective for encrypted mobile storage. Compared to flash management without deduplication, our lightweight, integrated approach reduced the total flash-block erase count by 48.7%, average write response time by 43.8%, and total energy consumption by 25.1% on average under the workloads of all the selected mobile applications.
Exploiting Page Correlations for Write Buffering in Page-Mapping Multichannel SSDs
(2016)
Huang, Sheng-Min
;
Chang, Li-Pin
;
資訊工程學系
;
Department of Computer Science
Advanced solid-state disks (SSDs) have been equipped with page-mapping flash translation layers and multichannel architectures. The SSDs employ a RAM-based write buffer, which delays write requests for reducing write traffic, reorders requests for mitigating garbage-collection overhead, and produces parallel page writes for improving channel time utilization. This work presents a novel write buffer algorithm that exploits temporal and spatial correlations among buffer pages. The write-buffer groups temporally or spatially correlate buffer pages and then write the grouped buffer pages to the same flash block. In this way, when the correlated page data are updated in the future, flash blocks will receive bulk page invalidations and become good candidates for garbage collection. With multichannel architectures, the write buffer adaptively disperses read-most sequential data over channels for high page-level parallelism of sequential reads, while clustering write-most sequential data in the same channel for a reduced cost of garbage collection. We evaluated the proposed method and previously proposed buffer algorithms. Our method was shown to outperform the existing methods by up to 134%. We also implemented our buffer design on the OpenSSD platform; the time and space overheads of our design were reported to be very low.
Plugging Versus Logging: Adaptive Buffer Management for Hybrid-Mapping SSDs
(2015-03-01)
Chang, Li-Pin
;
Su, Yo-Chuan
;
Wu, I-Chen
;
資訊工程學系
;
Department of Computer Science
A promising technique to improve the write performance of solid-state disks (SSDs) is to use a disk write buffer. The goals of a write buffer is not only to reduce the write traffic to the flash chips but also to convert host write patterns into long and sequential write bursts. This study proposes a new buffer design consisting of a replacement policy and a write-back policy. The buffer monitors how the host workload stresses the flash translation layer upon garbage collection. This is used to dynamically adjust its replacement and write-back strategies for a good balance between write sequentiality and write randomness. When the garbage collection overhead is low, the write buffer favors high write sequentiality over low write randomness. When the flash translation layer observes a high overhead of garbage collection, the write buffer favors low write randomness over high write sequentiality. The proposed buffer design outperformed existing approaches by up to 20% under various workloads and flash translation algorithms, as will be shown in experiment results.
Reducing Asynchrony in Channel Garbage-Collection for Improving Internal Parallelism of Multichannel Solid-State Disks
(2014-01-01)
Chang, Li-Pin
;
Wen, Chen-Yi
;
交大名義發表
;
National Chiao Tung University
Solid-state disks use multichannel architectures to boost their data transfer rates. Because realistic disk workloads have numerous small write requests, modern flash-storage devices adopt a write buffer and a set of independent channels for better parallelism in serving small write requests. When a channel is undergoing garbage collection, it stops responding to inbound write traffic and accumulates page data in the write buffer. This results in contention for buffer space and creates idle periods in channels. This study presents a channel-management strategy, called garbage-collection advancing, which allows early start of garbage collection in channels for increasing the overlap among channel activities of garbage collection and restoring the balance of buffer-space usage among channels. This study further introduces cycle filling, which is a version of garbage-collection advancing tailored for the operation model of flash planes. Experimental results show that the proposed methods greatly outperformed existing designs of multichannel systems in terms of response and throughput. We also successfully implemented the proposed methods in a real solid-state disk and proved their feasibility in real hardware.
Plugging Versus Logging: A New Approach to Write Buffer Management for Solid-State Disks
(2011)
Chang, Li-Pin
;
Su, You-Chiuan
;
資訊工程學系
;
Department of Computer Science
Using device write buffers is a promising technique to improve the write performance of solid-state disks. The write buffer not only reduces the write traffic to the flash but also produces large and sequential write bursts to the underlying flash translation layer. This study proposes a new buffer design consisting of a replacement policy and a write-back policy. This buffer monitors how the host workload stresses the flash translation layer upon garbage collection, and dynamically adjusts its replacement and write-back strategies for a good balance between write sequentiality and traffic reduction. Experimental results show that the proposed buffer design outperformed existing approaches by up to 20% under various workloads and flash translation algorithms.

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