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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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Adaptive Write Interference Management with Efficient Mapping for Shingled Recording Disks
(2019-01-01)
Lee, Ming-Chang
;
Chang, Li-Pin
;
Wu, Sung-Ming
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Yui, Wei-Shang
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資訊工程學系
Shingled Magnetic Recording (SMR) is a novel disk technology that partially overlaps adjacent disk tracks for high storage density. The partial overlap creates write interference between tracks, and overwriting a track requires to rewrite all its downstream tracks. Inspired by the highly unequal track modify probabilities under real workloads, we propose moving frequently modified tracks toward a downstream, deliberately reserved track, called a guard track, to reduce the extent of write interference. We also introduce a low-cost, seek-optimized scheme for efficient logical-to-physical address mapping. Experimental results showed that our approach outperformed a popular design by 54% and 55% on average in terms of write response time and total disk writes, respectively.
Current-Aware Flash Scheduling for Current Capping in Solid State Disks
(2020-02-01)
Chang, Li-Pin
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Cheng, Chia-Hsiang
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Chang, Shu-Ting
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Chou, Po-Han
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資訊工程學系
Solid state disks (SSDs) employ internal parallelism to boost their input/output (I/O) performance, but a high degree of flash parallelism inevitably consumes a high level of current. To budget power or support multiple power sources, system software may force an SSD into a new power mode that has a specific current supply limit. This paper introduces a firmware approach to optimize SSD internal parallelism subject to a current supply limit. The proposed method involves two steps. First, we constructed current models of flash operations on the basis of real-world measurement results. Second, we designed a firmware scheduler to determine the actual starting time of each flash operation. The proposed scheduler accounted for flash aging, process variation, and internal resource contention, and it avoided any current cap violation by checking a few time points instead of every unit of time. Our experimental results indicated that the proposed approach outperformed existing methods with respect to I/O response time and throughput under realistic workloads.
File Fragmentation in Mobile Devices: Measurement, Evaluation, and Treatment
(2019-09-01)
Ji, Cheng
;
Chang, Li-Pin
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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.
A Low-Cost Wear-Leveling Algorithm for Block-Mapping Solid-State Disks
(2011-01-01)
Chang, Li-Pin
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Huang, Li-Chun
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資訊工程學系
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Department of Computer Science
Multilevel flash memory cells double or even triple storage density, producing affordable solid-state disks for end users. However, flash lifetime is becoming a critical issue in the popularity of solid-state disks. Wear-leveling methods can prevent flash-storage devices from prematurely retiring any portions of flash memory. The two practical challenges of wear-leveling design are implementation cost and tuning complexity. This study proposes a new wear-leveling design that features both simplicity and adaptiveness. This design requires no new data structures, but utilizes the intelligence available in sector-translating algorithms. Using an on-line tuning method, this design adaptively tunes itself to reach good balance between wear evenness and overhead. A series of trace-driven simulations show that the proposed design outperforms a competitive existing design in terms of wear evenness and overhead reduction. This study also presents a prototype that proves the feasibility of this wear-leveling design in real solid-state disks.
Lightweight, Integrated Data Deduplication for Write Stress Reduction of Mobile Flash Storage
(2018-11-01)
Yen, Miao-Chiang
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Chang, Shih-Yi
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Chang, Li-Pin
;
資訊工程學系
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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.
A Hybrid Approach to NAND-Flash-Based Solid-State Disks
(2010-10-01)
Chang, Li-Pin
;
資訊工程學系
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Department of Computer Science
Replacing power-hungry disks with NAND-flash-based solid-state disks (SSDs) is a recently emerging trend in flash-memory applications. One important SSD design issue is achieving a good balance between cost, performance, and lifetime. This study introduces a hybrid approach to large SSDs that combines MLC NAND flash and SLC NAND flash. Each of these flash architectures has its own drawbacks and benefits, and this study proposes that the two can complement each other. However, there are technical challenges pertaining to data placement, data migration, and wear leveling in heterogeneous NAND flash. The experimental results of our study show that combining 256 MB SLC flash with 20 GB MLC flash produces a hybrid SSD. This hybrid SSD is 1.8 times faster than a purely MLC-flash-based SSD in terms of average response time and improves energy consumption by 46 percent. The proposed hybrid SSD costs only four percent more than a purely MLC-flash-based SSD. The extra cost of a hybrid SSD is very limited and rewarding.
Improving File System Performance of Mobile Storage Systems Using a Decoupled Defragmenter
(2017-01-01)
Hahn, Sangwook Shane
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Lee, Sungjin
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Ji, Cheng
;
Chang, Li-Pin
;
Yee, Inhyuk
In this paper, we comprehensively investigate the file fragmentation problem on mobile flash storage. From our evaluation study with real Android smartphones, we observed two interesting points on file fragmentation on flash storage. First, defragmentation on mobile flash storage is essential for high I/O performance on Android smartphones because file fragmentation, which is a recurring problem (even after defragmentation), can significantly degrade I/O performance. Second, file fragmentation affects flash storage quite differently than HDDs. When files are fragmented on flash storage, the logical fragmentation and the physical fragmentation are de coupled and a performance degradation mostly comes from logical fragmentation. Motivated by our observations, we propose a novel defragger, Janus defragger (janusd), which supports two defraggers, janusdL for a logical defragger and janusdP for a physical defragger. JanusdL, which takes advantage of flash storage's internal logical to physical mapping table, supports logical defragmentation without data copies. JanusdL is very effective for most fragmented files while not sacrificing the flash lifetime. JanusdP, which is useful for physically fragmented files but requires data copies, is invoked only when absolutely necessary. By adaptively selecting janusdL and janusd P, janusd achieves the effect of full file defragmentation without reducing the flash lifetime. Our experimental results show that janusd can achieve at least the same level of I/O performance improvement as e4defrag without affecting the flash lifetime, thus making janusd an attractive defragmentation solution for mobile flash storage.
Dual Greedy: Adaptive Garbage Collection for Page-Mapping Solid-State Disks
(2012-01-01)
Lin, Wen-Huei
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Chang, Li-Pin
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資訊工程學系
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Department of Computer Science
In the recent years, commodity solid-state disks have started adopting powerful controllers and implemented page-level mapping for flash management. However, many of these models still use primitive garbage-collection algorithms, because prior approaches do not scale up with the dramatic increase of flash capacity. This study introduces Dual Greedy for garbage collection in page-level mapping. Dual Greedy identifies page-accurate data hotness using only block-level information, and adaptively switches its preference of victim selection between block space utilization and block stability. It can run in constant time and use very limited RAM space. Our experimental results show that Dual Greedy outperforms existing approaches in terms of garbage-collection overhead, especially with large flash blocks.
I/O Scheduling with Mapping Cache Awareness for Flash Based Storage Systems
(2016-01-01)
Ji, Cheng
;
Wu, Chao
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Chang, Li-Pin
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Shi, Liang
;
Xue, Jason
NAND flash memory has been the default storage component in mobile systems. One of the key technologies for flash management is the address mapping scheme between logical addresses and physical addresses, which deals with the inability of in-place-updating in flash memory. Demand-based page-level mapping cache is often applied to match the cache size constraint and performance requirement of mobile storage systems. However, recent studies showed that the management overhead of mapping cache schemes is sensitive to the host I/O patterns, especially when the mapping cache is small. This paper presents a novel I/O scheduling scheme, called MAP, to alleviate this problem. The proposed scheduling approach reorders I/O requests for performance improvement from two angles: Prioritizing the requests that will hit in the mapping cache, and grouping requests with related logical addresses into large batches. Experimental results show that MAP improved upon traditional I/O schedulers by 30% and 8% in terms of read and write latencies, respectively.
Detecting Solid-State Disk Geometry for Write Pattern Optimization
(2011-01-01)
Kuo, Chun-Chieh
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Hsieh, Jen-Wei
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Chang, Li-Pin
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交大名義發表
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National Chiao Tung University
Solid-state disks use flash memory as their storage medium, and adopt a firmware layer that makes data mapping and wear leveling transparent to the hosts. Even though solid-state disks emulate a collection of logical sectors, the I/O delays of accessing all these logical sectors are not uniform because the management of flash memory is subject to many physical constraints of flash memory. This work proposes a collection of black-box tests can detect the geometry inside of a solid-state disk. The host system software can arrange data in the logical disk space according to the detected geometry information to match the host write pattern with the device characteristic for reducing the flash management overhead in solid-state disks.

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