• The KIPS Transactions:PartA
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• v.13A no.5 s.102
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• pp.387-398
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• 2006

In this paper, we propose a new page allocation scheme for flash memory file system. The proposed scheme allocates pages by exploiting the concept of Purity, which is defined as the fraction of blocks where valid Pages and invalid Pages are coexisted. The Pity determines the cost of block cleaning, that is, the portion of pages to be copied and blocks to be erased for block cleaning. To enhance the purity, the scheme classifies hot-modified data and cold-modified data and allocates them into different blocks. The hot/cold classification is based on both static properties such as attribute of data and dynamic properties such as the frequency of modifications. We have implemented the proposed scheme in YAFFS and evaluated its performance on the embedded board equipped with 400MHz XScale CPU, 64MB SDRAM, and 64MB NAND flash memory. Performance measurements have shown that the proposed scheme can reduce block cleaning time by up to 15.4 seconds with an average of 7.8 seconds compared to the typical YAFFS. Also, the enhancement becomes bigger as the utilization of flash memory increases.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.1
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• pp.17-22
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• 2010

As deployments of Flash memory are spreading out rapidly from tiny USB storages to large DB servers, interoperability become an indispensable requirement for Flash memory software architecture. For the purpose, many systems make use of the conventional FAT file system and FTL (Flash Translation Layer) software as a de facto standard. However, the tactless combination of the FAT file system and FTL does not satisfy diverse other requirements of a variety of systems. In this paper, we propose a novel reconfigurable integrated Flash memory software architecture, named INFLAWARE (INtegrated FLAsh softWARE) that supports not only interoperability but also reconfigurability and performance enhancement. Real implementation based experimental results have shown that INFLAWARE can achieve improvements of memory footprint up to 27% with an average of 19%, compared with the conventional FAT and FTL combination. Also, by using map_destroy technique, it can reduce response times of various applications up to 21% with an average of 10%.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.3
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• pp.191-198
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• 2009

The FAT (File Allocation Table) compatible file system has been widely used in mobile devices and memory cards because of its data exchangeability among numerous platforms recognizing the FAT file system. By the way. modern embedded systems have tough demands for instant power failure recovery and superior performance for multimedia applications. The key issue is how to achieve the goals of superior write performance and instant booting capability while controlling compatibility issues. To achieve the goals while controlling compatibility issues. we devised a temporary meta-data journaling scheme for a FAT compatible file system. Benchmark results of the scheme implemented in a FAT compatible file system shows that it really improves write performance of the FAT file system by converting small random write for meta-data update to a large sequential write in journaling area. Also, it provides natural way to implement the instant booting capability. Nevertheless, the file system compatibility is temporarily compromised by the scheme because it stores updated meta-data in the temporary journaling area rather than to their original locations. However, the compatibility can be fully recovered at any time by journal-flushing that copies meta-data in journaling area to their original locations. Generally, the journal-flushing is done before un-mounting a memory card so that it can be used in other mobile devices which recognized FAT file system but not the temporary meta-data journaling scheme.

• Journal of KIISE:Computing Practices and Letters
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• v.13 no.6
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• pp.422-426
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• 2007

Personal mobile devices equipped with non-volatile storage such as MP3 player, PMP, cellular phone, and USB memory require safety for the stored data on the devices. One of the safety requirements is secure deletion, which is removing stored data completely so that the data can not be restored illegally. In this paper, we study how to design the secure deletion on Flash memory, commonly used as storage media for mobile devices. We consider two possible secure deletion policy, named zero-overwrite and garbage-collection respectively, and analyze how each policy affects the performance of Flash memory file systems. Then, we propose an adaptive file deletion scheme that exploits the merits of the two possible policies. Specifically, the proposed scheme applies the zero-overwrite policy for small files, whereas it employs the garbage-collection policy for large files. Real implementation experiments show that the scheme is not only secure but also efficient.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.647-648
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• 2008

Traditional FTL and flash file systems based of NAND flash memory may not be adaptively applied to new fusion flash memory which combines the advantages of NAND and NOR flash memory. In this paper, we propose a FTL performance measurement tool using Multi Block Erase function of fusion flash memory. The performance measurement tool shows that multi block erase function can be effectively utilized in performance enhancement of garbage collection for fusion flash memory.

• Journal of KIISE
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• v.42 no.4
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• pp.427-433
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• 2015

The rapid advancement of computing technology has triggered the need for fast data I/O processing and high-performance storage technology. Next generation memory technology, which we refer to as new memory, is anticipated to be used for high-performance storage as they have excellent characteristics as a storage device with non-volatility and latency close to DRAM. This research proposes NTL (New memory Translation layer) as a technology to make use of new memory as storage. With the addition of NTL, conventional I/O is served with existing mature disk-based file systems providing compatibility, while new memory I/O is serviced through the NTL to take advantage of the byte-addressability feature of new memory. In this paper, we describe the design of NTL and provide experiment measurement results that show that our design will bring performance benefits.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.6
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• pp.543-556
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• 2009

Recently, NAND flash memory is being used as the swap device of virtual memory as well as the file storage of mobile systems. Since temporal locality is dominant in page references of virtual memory, LRU and its approximated CLOCK algorithms are widely used. However, cost of a write operation in flash memory is much larger than that of a read operation, and thus a page replacement algorithm should consider this factor. This paper analyzes virtual memory read/write reference patterns individually, and observes the ranking inversion problem of temporal locality in write references which is not observed in read references. With this observation, we present a new page replacement algorithm considering write frequency as well as temporal locality in estimating write reference behaviors. This new algorithm dynamically allocates memory space to read/write operations based on their reference patterns and I/O costs. Though the algorithm has no external parameter to tune, it supports optimized implementations for virtual memory systems, and also performs 20-66% better than CLOCK, CAR, and CFLRU algorithms.

• The KIPS Transactions:PartA
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• v.9A no.4
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• pp.399-404
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• 2002

Along the evolution of information and communication technologies, manufacturing embedded systems such as PDA (personal digital assistant), HPC (hand -held PC), settop box. and information appliance became realistic. And RTOS (real-time operating system) and filesystem have been played essential re]os within the embedded systems as well. For the filesystem of embedded systems, flash memory has been used extensively instead of traditional hard disk drives because of embedded system's requirements like portability, fast access time, and low power consumption. Other than these requirements, nonvolatile storage characteristic of flash memory is another reason for wide adoption in industry. However, there are some technical challenges to cope with to use the flash memory as an indispensable component of the embedded systems. These would be relatively slow cleaning time and the limited number of times to write-and-clean. In this paper, a new cleaning policy is proposed to overcome the problems mentioned above and relevant performance comparison results will be provided. Ranking cleaning policy(RCP) decides when and where to clean within the flash memory considering the cost of cleaning and the number of times of cleaning. This method will maximize not only the lifetime of flash memory but also the performance of access time and manageability. As a result of performance comparison, RCP has showed about 10 ~ 50% of performance evolution compared to traditional policies, Greedy and Cost-benefit methods, by write throughputs.

• IEMEK Journal of Embedded Systems and Applications
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• v.2 no.1
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• pp.1-8
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• 2007

In this paper, we developed a file system architecture for portable multimedia devices. To enhance user convenience, the information about the stored files should be easily retrieved and organized. We defined NMD (Networked MetaData), which can organize the files in networked fashion by attaching user-defined attributes and relation between files. The NMD is stored in flash memory to utilize its nonvolatile property and low-power consumption, while multimedia files are stored in hard disk, an inexpensive mass storage. The experimental implementation showed that this architecture was able to save about 10% power compared to the hard disk NMD-store.

• IEMEK Journal of Embedded Systems and Applications
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• v.14 no.5
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• pp.249-258
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• 2019

In the cyber-physical system, big data collected from numerous sensors and IoT devices is transferred to the Cloud for processing and analysis. When transferring data to the Cloud, merging data into one single file is more efficient than using the data in the form of split files. However, current merging and splitting operations are performed at the user-level and require many I / O requests to memory and storage devices, which is very inefficient and time-consuming. To solve this problem, this paper proposes kernel-level partitioning and combining operations. At the kernel level, splitting and merging files can be done with very little overhead by modifying the file system metadata. We have designed the proposed algorithm in detail and implemented it in the Linux Ext4 file system. In our experiments with the real Cloud storage system, our technique has achieved a transfer time of up to only 17% compared to the case of transferring split files. It also confirmed that the time required can be reduced by up to 0.5% compared to the existing user-level method.