• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.12
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• pp.2202-2211
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• 2006

EXT3NS is a special-purpose file system for large scale multimedia streaming servers. It is built on top of streaming acceleration hardware device called Network-Storage card. The EXT3NS file system significantly improves streaming performance by eliminating memory-to-memory copy operations, i.e. sending video/audio from disk directly to network interface with no main memory buffering. In this paper, we design and implement a buffer cache mechanism, called PMEMCACHE, for EXT3NS file system. We also propose a buffer cache replacement method called ONS for the buffer cache mechanism. The ONS algorithm outperforms other existing buffer replacement algorithms in distributed multimedia streaming environment. In EXT3NS with PMEMCACHE, operation is 33MB/sec and random read operation is 2.4MB/sec. Also, the buffer replacement ONS algorithm shows better performance by 600KB/sec than other buffer cache replacement policies. As a result PMEMCACHE and an ONS can greatly improve the performance of multimedia steaming server which should supportmultiple client requests at the same time.

• Journal of Advanced Navigation Technology
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• v.17 no.1
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• pp.39-46
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• 2013

If a file system is damaged because of the unusual system close, the system performs the consistency test using fsch and it takes long time. Especially, if it is a big file system, it will take a lot of time. The journaling file system that uses journaling technique, can reduce the restoring time because it uses meta data and it may increase the chance of restoration when restoring. The goal of this paper compared performance evaluation journaling file systems focused on the reading and writing using Iozone tool which is the kernel based benchmarking tool in linux operating system. In this paper, Ex4 which is the current basic Linux file system. is 1.28x faster than XFS file system in terms of file read performance and 1.22x faster than Ext3 file system in terms of file write performance.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.3
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• pp.21-28
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• 2016

File Time information has a significant meaning in digital forensic investigation. File time information in Linux Ext4 (Extended File System 4) environment is the Access Time, Modification Time, Inode Change Time, Deletion Time and Creation Time. File time is variously changed by user manipulations such as creation, copy and edit. And, the study of file time change is necessary for evidence analysis. This study analyzes the change in time information of files or folders resulting from user manipulations in Linux operating system and analyzes ways to determine real time of malware infection and whether the file was modulation.

• The KIPS Transactions:PartA
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• v.16A no.2
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• pp.101-112
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• 2009

Existing techniques for defragmentation of the file system need intensive disk operation for some periods at specific time such as disk defragmentation program. In this paper, for solving this problem, we design and implement the automatic and continuous defragmentation free system by distributing the disk operation. We propose the Automatic Layout Scoring(ALS) mechanism for measuring defragmentation degree and suggest the Lazy Copy mechanism that copies the defragmented data at idle time for scattering the disk operation. We search the defragmented file by Automatic Layout Scoring mechanism and then find for empty spaces for that searched file. After lazy copy of searched fils to empty space for preventing that file from being lost, the algorithm solves the defragmentation problem by updating the I-node of that file. We implement these algorithms in Linux and evaluate them for small and defragmented file to get the layout scoring. We outperform the Linux EXT2 file system by $2.4%{\sim}10.4%$ in layout scoring evaluation. And the performance of read and write for various file size is better than the EXT2 by $1%{\sim}8.5%$ for write performance and by $1.2%{\sim}7.5%$ for read performance. We suggest this system for solving the problem of defragmentation automatically without disturbing the I/O task and manual management.

• Review of KIISC
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• v.29 no.6
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• pp.13-22
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• 2019

기존의 NTFS, HFS+, Ext4와 같은 전통적인 파일시스템들은 디스크 사용, 공간 관리, 데이터 암호화 등 여러 측면에서 한계점을 가지고 있었다. 특히 디스크 사용 측면에서 기본적으로 단일 디스크 안에서 동작하도록 설계되었기 때문에 여러 개의 디스크에서 동작하도록 하려면 RAID와 같은 별도의 구성이 필요했다. 이에 따라 주요 운영체제들은 위와 같은 기존 파일시스템들의 한계점들을 극복하도록 설계된 Pooled Storage 파일시스템들을 공개하였다. Pooled Storage 파일시스템에 관한 연구는 2017년 여름 미국 오스틴에서 열린 DFRWS 학회에서 독일의 Jan-Niclas Hilgert에 의해 발표된 이후 디지털 포렌식 학계 및 산업계에서 집중적인 연구개발이 진행되고 있다. 2017년 Hilgert는 ZFS 파일시스템에 대한 분석기능을 공개소프트웨어인 SleuthKit에 추가한 기술을 발표하였고, 2018년 DFRWS에서는 BtrFS 파일시스템에 대한 분석기능을 공개하였다. BlackBag Technologies의 Joe Syle은 APFS 파일시스템에 대한 분석기능을 SleuthKit에 추가한 결과를 DFRWS 2018에서 발표하였다. 노르웨이의 Rune Nordvik은 2019년 DFRWS에서 REFS를 역공학을 통하여 분석한 결과를 공개하였다. 국내에서는 고려대학교를 중심으로 ReFS에 대한 연구가 진행 중이다. 본 논문에서는 주요 운영체제들이 공개한 Pooled Storage 파일시스템 형태의 차세대 파일시스템인 ReFS, APFS, BtrFS를 소개하고 각 파일시스템의 특징과 주요 기능들을 설명한다.

• Journal of Internet Computing and Services
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• v.4 no.2
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• pp.11-19
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• 2003

The technique which stores cache data in EXT2 or UFS designed for general purpose is not suitable for satisfying the speed required for web cache due to the general purpose file system. This study shows that there is the better solution by optimizing the file system using the characteristics of web file. It is impossible that the suggested RawCFS changes the size of cached object and the access authentication, and this results from the existence of up-to-dated object in the original server. This file system is proved in the capability test that it is faster than the technique by 40% which stores in each file by object unit. This can be used in the design of high end web server such as shoppingmall or Internet Broadcasting station which should provide objects like image or HTML as well as cache server to the client for the fast service.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.3
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• pp.107-111
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• 2023

Journaling techniques are widely used to maintain a consistent file system state in the event of a system crash. As existing journaling techniques are designed for block storage such as HDDs, they are not efficient for byte-addressable persistent memory media. This paper proposes a metadata journaling technique for in-memory file systems that has the ability of avoiding inconsistent file system states in crash situations. The proposed journaling technique reduces a large amount of writing by making use of the byte-addressable feature of memory media and bypasses heavy software I/O stack. Experimental results with the IOzone benchmark show that the proposed journaling technique improves the performance of Ext4 by 49.2% on average.

• Journal of IKEEE
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• v.23 no.1
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• pp.80-90
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• 2019

Even though Non-Volatile Memory (NVM) is used for data storage, a page table should be built to access data in it. And this observation leads us to the Persistent Page Table (PPT) scheme that keeps the page table in NVM persistently. By the way, processors have different page table structures and really operational page table cannot be built without virtual and physical addresses of NVM. However, those addresses are determined dynamically when NVM storage is attached to the system. Thus, the PPT should have system-independent and also address-independent structure and really working system-dependent page table should be built from the PPT. Moreover, entries of PPT should be updated atomically and, in this paper, we describe the design of PPT that meets those requirements. And we investigate how file systems can decrease the journaling overhead with the swap operation, which is a new operation created by the PPT. We modified the Ext4 file system in Linux and experiments conducted with Filebench workloads show that the swap operation enhances file system performance up to 60%.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.376-378
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• 2012

중앙 처리장치, 주기억장치, 보조기억장치로 이어지는 현재의 컴퓨터 구조에서 비휘발성 메모리 소자의 발전으로 주기억장치를 비휘발성 메모리 소자로 대체하는 컴퓨터 시스템의 변화가 요구되고 있다. 이런 흐름에 맞춰 주기억장치에 기반한 새로운 파일시스템을 제시한다. 또한 새롭게 제시된 파일시스템과 유사한 tmpfs를 이용하여 기존의 시스템에 쓰이던 ext4fs와 비교하여 성능의 향상을 확인한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2016.10a
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• pp.16-17
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• 2016

일반적인 에디터 프로그램과 운영체제를 사용하여 데이터를 편집할 경우, 일부 수정에도 모든 데이터를 다시 저장하고 있다. 본 논문에서는 이러한 기존 파일시스템의 문제점을 개선하기 위해 가변 길이 블록의 개념을 커널 레벨에 적용하여 효율적으로 수정된 데이터를 다시 쓸 수 있도록 하였다. 가변 블록은 데이터 삭제가 발생 했을 경우 나머지 블록은 그대로 유지하고 수정된 블록만 다시 저장하며, 삭제된 데이터로 인해 생기는 빈 공간의 그대로 유지하는 방법을 말한다. 이 개념을 기존 리눅스에서 사용하는 ext4파일 시스템에 적용하여 시스템을 구축, 실험하였으며 결과적으로 쓰기 연산을 비롯해 CPU사용량에서 크게 성능을 향상시켰다.