• Journal of the Korea Institute of Information Security & Cryptology
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• v.23 no.3
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• pp.417-429
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• 2013

A lot of OS(Operating Systems) such as Linux and Android selected Ext4 as the official file system. Therefore, a recovery of deleted file from Ext4 is becoming a pending issue. In this paper, we suggest how to recover the deleted file by analyzing the entire structure of Ext4 file system, the study of metadata area, the distinct feature when file is assigned and deleted. Particularly, we focus on studying the features of file which is assigned in Ext4 file system in Android OS and also suggest the method to recover the deleted file that is fragmented from the un-allocated area.

• The Journal of the Korea Contents Association
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• v.18 no.4
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• pp.178-185
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• 2018

Recently, demands for computer systems with multicore CPUs and high-performance flash-based storage devices (i.e., flash SSD) have rapidly grown in cloud computing, surer-computing, and enterprise storage/database systems. Journaling file systems running on high-performance systems do not exploit the full I/O bandwidth of high-performance SSDs. In this article, we evaluate and analyze the performance of the Linux EXT4 file system with high-performance SSDs and multicore CPUs. The system used in this study has 72 cores and Intel NVMe SSD, and the flash SSD has performance up to 2800/1900 MB/s for sequential read/write operations. Our experimental results show that checkpointing in the EXT4 file system is a major overhead. Furthermore, we optimize the checkpointing procedure and our optimized EXT4 file system shows up to 92% better performance than the original EXT4 file system.

• KIISE Transactions on Computing Practices
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• v.21 no.1
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• pp.52-57
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• 2015

In this paper, we analyze the performance of the TRIM commands on various SSDs and, based on our analysis results, we enhance the performance of these TRIM commands in the Ext4 file system. We observed that the performance of the TRIM commands improves as the size of the LBA-range increases, the sector number is aligned and continuous or more LBA-ranges are notified via a single TRIM command. However, although the performance is better when multiple LBA-ranges are informed by a single TRIM command, the Ext4 file system issues a single TRIM command for every LBA-range. In this paper, we modify the Ext4 file system to convey at most 64 LBA-ranges per TRIM command. Evaluations through Filebench show that the performance of file deletion operations is improved by up to 35%.

• Journal of KIISE
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• v.44 no.4
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• pp.363-373
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• 2017

Ext4 file system is widely used in various computing environments such as those of the PC, the server, and the Linux-based embedded system. Ext4, which uses a buffer for block I/O, provides fsync() system call to applications to guarantee the consistency of a specific file. A log of the analytical studies regarding the operation of Ext4 and the improvement of its performance has been compiled, but it has not been studied in detail in terms of kernel versions. We figure out that the behavior of fsync() system call is different depending on the kernel version. Between the kernel versions of 3.4.0 and 4.7.2, 3.4.0, 3.8.0, and 4.6.2 showed behavioral differences regarding the fsync() system call. The latency of fsync() in kernel 3.4.0 is longer than that of the more-advanced 3.7.10; meanwhile, the characteristics of 3.8.0 enabled the disruption of the Ext4 journaling order, but the ordered defect was solved with 4.6.2.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.89-91
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• 2012

플래시 저장장치는 순차 쓰기패턴에 높은 성능을 보이고, 랜덤 쓰기패턴에 낮은 성능을 보인다고 알려져 있다. 그러나 실제 응용 프로그램은 동작 방식에 따라 복합적인 패턴을 보일 수 있다. 본 논문은 대표적인 모바일 응용으로서 웹 브라우저 응용의 파일시스템 접근 특성을 정량적으로 분석하고자 한다. 최근에 안드로이드 스마트 폰에 채택된 Ext4 파일시스템을 기준으로 웹 브라우저 응용의 파일시스템 요청들을 성능개선점을 지적하고자 한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2015.10a
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• pp.1268-1271
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• 2015

전 세계 주요 56개국 성인 인구의 스마트폰 보급률이 평균 약 60%에 달하고. 지난 월 기준 한국 스마트폰의 보급률은 83.0%에 달해 세계 4위를 기록하였다. 안드로이드, iOS를 포함한 대부분의 모바일 플랫폼은 SQLite 데이터베이스를 기본 데이터베이스로 사용하고 있는 것으로 알려져 있다. 현재 보급된 대부분의 스마트폰의 저장장치는 플래시 메모리를 기반으로 하고 있다. 그러나 현재까지 안드로이드 운영체제의 기본 파일시스템은 Ext4 파일시스템으로 알려져 있으며, 플래시메모리에 최적화되었다고 주장하는 다른 파일시스템에 대한 성능 평가 및 데이터 입출력 특징의 자세한 분석 연구는 존재하지 않았다. 본 논문에서는 가장 잘 알려진 파일 시스템 Ext4, XFS, Btrfs 세 종류에서 실제 안드로이드 애플리케이션 쿼리를 사용하여 성능 측정을 진행하였다. 실험 결과 기본 파일 시스템으로 사용되고 있는 Ext4가 가장 빠른 성능을 나타낸 것을 확인하였고, 각 파일시스템마다 완연히 다른 데이터 입출력 특징을 갖고 있는 것을 확인하였다.

• Journal of Information Technology Applications and Management
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• v.10 no.4
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• pp.169-183
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• 2003

In multimedia systems, very large files are stored and played. Because those files are read-centric and have low reusability, legacy file systems that are optimized for the use of many small files, do not show good performance in the multimedia systems. We implemented a new file system to deal with those characteristics. The new file system shows the superior performances in read, write and mixed operation to the Linux's EXT2 or EXT3 file systems. The new file system was implemented on the Linux operating system, and it also can be easily ported to other operating systems.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.193-194
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• 2009

멀티미디어 장치의 대중화로 인해 사용자는 고화질의 영상과 다양한 멀티미디어 응용 서비스에 대한 요구가 증가하고 있다. 고화질의 미디어 컨텐츠는 대용량 파일의 형태로 저장된다. 대용량 파일의 필요한 부분만을 편집하여 재 저장하기 위해서는 새로운 기법이 요구된다. 현재의 리눅스 시스템에서는 편집된 파일의 내용을 새롭게 저장하는 방법을 사용하는데 미디어 컨텐츠와 같은 대용량 파일의 경우 많은 디스크 대역폭과 시간을 요구한다. 본 논문에서는 리눅스 Ext4 파일 시스템에서 범위 지정을 통한 고속 편집 저장 방법을 제안한다. 본 기법은 실제 데이터의 디스크 I/O 없이 메타데이터 편집만을 통해 대용량 멀티미디어 파일 편집 저장을 가능하게 한다.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.4
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• pp.88-95
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• 2010

As the development of IT technologies, storages stored very sensitive data which should not be damaged, too. It increased the importance of data backup and makes the time need to backup data important issues. Snapshot is one of the backup technologies which needs short downtime to maintain consistency of data during backup data. In this paper, we studied two kinds of snapshots, local file system based snapshot and network file system based snapshot. In the local file system based snapshot part, we propose the PSnap which is a snapshot library for non-snapshot file system as like Ext2, Ext3 and XFS. In another part, network file system based snapshot, we propose the GlorySnap which snapshot utilities for GloryFS is a distributed file system was made by ETRI.

• The Journal of the Korea Contents Association
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• v.20 no.8
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• pp.368-374
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• 2020

Journaling file systems (JFS) manage changes of file systems not yet committed in a data structure known as a journal to restore the file system in the event of an unexpected failure. Extra write operations required for journaling negatively affect the performance of JFS. The high-performance and byte-addressable non-volatile memory (NVM) was expected to easily mitigate these performance problems by providing NVM space as journal storage. However, even with such non-volatile memory technologies, performance problems still arise due to scalability problems inherent in processing transactions of JFS. To solve this problem, we proposes a technique for processing file system transactions for scalable performance. To this end, lock-free data structures are used and multiple I/O requests are allowed to simultaneously be processed on high-performance storage devices with multiple I/O channels. We evaluate the file system with the proposed technique by comparing the original ext4 file system and the recent proposed NVM-based journaling file system on a multi-core server, and experimental results show that our file system has better performance (up-to 2.9/2.3 times) than the original ext4 file system and the recent NVM-based journaling file system, respectively.