• Journal of KIISE:Computing Practices and Letters
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• v.11 no.4
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• pp.305-311
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• 2005

Flash memory software running on cellular phones and PDAs need to be tested extensively to cope with abrupt power and media faults. For those tests, we designed and implemented a Flash memory emulator with fault injection features. The fault injection tester has provided a helpful framework for designing fault recovery schemes and also for analyzing fault damages to the FTL (Flash Translation Layer) and file system for a Flash memory based system. In this paper, we discuss Plash memory fault types and fault injection features implemented on this Flash memory emulator. We then discuss in detail a design flaw revealed during fault injection tests. Specifically, it was revealed that a scheme that was believed to improve reliability instead, turned out to be harmful. In addition, we discuss post-fault behaviors of the FTL and the file system.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.10
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• pp.21-30
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• 1994

We discussed the Distributed Control System's design on preface and analyzed time of the real-time communication by using designed system. The DCS proposed in this thesis was implemented to network file system having recovery advantage and shared memory method to access file system of a Remote Station with ease. Also, this system minimized the network delay-time by using the real-time VME147 board. In implemented DCS, the performance analysis of real-time process of a Remote Station was done to get the total time for reak-tune communication from a Remote Station to the Central Station after terminating of process. For the analysis of system performance, we experiented by three steps. Firstly, we measuredthe processing the of LOOP function that real-time CPU convertes to-2,500~10.000 values from the input data of the Analog Interface Card. Secondly, we measured the processing time of the LOGIC function and the LOOP function. Lastly, we measured total processing time for communication from a Remote Station to the Centrol Station.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.2
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• pp.189-196
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• 2020

In general, fragmented files without signatures and file meta-information are difficult to recover. Multimedia files, in particular, are highly fragmented and have high entropy, making it almost impossible to recover with signature-based carving at present. To solve this problem, research on fragmented files is underway, but research on multimedia files is lacking. This paper is a study that classifies the types of fragmented multimedia files without signature and file meta-information. Extracts the characteristic values of each file type through the frequency differences of specific byte values according to the file type, and presents a method of designing the corresponding Gray-Scale table and classifying the file types of a total of four multimedia types, JPG, PNG, H.264 and WAV, using the CNN (Convolutional Natural Networks) model. It is expected that this paper will promote the study of classification of fragmented file types without signature and file meta-information, thereby increasing the possibility of recovery of various files.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2784-2790
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• 2015

The column-oriented database storage is a very advanced model for large-volume data transactions because of its superior I/O performance. Traditional data storages exploit row-oriented storage where the attributes of a record are placed contiguously in hard disk for fast write operations. However, for search-mostly data warehouse systems, column-oriented storage has become a more proper model because of its superior read performance. Recently, solid state drive using flash memory is largely recognized as the preferred storage media for high-speed data analysis systems. In this research, we propose a new transaction recovery scheme for a column-oriented database environment which is based on a flash media file system. We improved traditional shadow paging schemes by reusing old data pages which are supposed to be invalidated in the course of writing a new data page in the flash file system environment. In order to reuse these data pages, we exploit reused shadow list structure in our column-oriented shadow recovery(CoSR) scheme. CoSR scheme minimizes the additional storage overhead for keeping shadow pages and minimizes the I/O performance degradation caused by column data compression of traditional recovery schemes. Based on the results of the performance evaluation, we conclude that CoSR outperforms the traditional schemes by 17%.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.2
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• pp.357-367
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• 2018

As information technology of modern society develops, various malicious codes with the purpose of seizing or destroying important system information are developing together. Among them, ransomware is a typical malicious code that prevents access to user's resources. Although researches on detecting ransomware performing encryption have been conducted a lot in recent years, no additional methods have been proposed to recover damaged files after an attack. Also, because the similarity comparison technique was used without considering the repeated encryption, it is highly likely to be recognized as a normal behavior. Therefore, this paper implements a filter driver to control the file system and performs a similarity comparison method that is verified based on the analysis of the encryption pattern of the ransomware. We propose a system to detect the malicious process of the accessed process and recover the damaged file based on the cloud storage.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.2
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• pp.85-91
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• 2014

Cloud storage system uses a distributed file system for storing and managing data. Traditional distributed file system makes a triplication of data in order to restore data loss in disk failure. However, enforcing data replication method increases storage utilization and causes extra I/O operations during replication process. In this paper, we propose a data replication method using erasure codes in cloud storage system to improve storage space efficiency and I/O performance. In particular, according to data access frequency, the proposed method can reduce the number of data replications but using erasure codes can keep the same data recovery performance. Experimental results show that proposed method improves performance in storage efficiency 40%, read throughput 11%, write throughput 10% better than HDFS does.

• Proceedings of the Korean Information Science Society Conference
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• 2004.04a
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• pp.244-246
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• 2004

사용자는 침입이 있더라도 항상 신뢰성 있는 정보를 획득하길 원하기 때문에 침입에 의하여 파일이 훼손되는 경우에도 사용자에게 투명한 방법으로 복구할 수 있는 방법이 필요하다. 본 논문에서는 리눅스 기반의 파일 시스템에서 변경이 일어날 때마다 로그 형태로 저장된 로그 파일을 이용하여 침입에 의하여 훼손된 부분을 복구하기 위한 모듈을 구현하고, 시험을 통하여 로그 기반 침입 복구 모듈을 적재한 시스템에서 로그를 관리하기 위해 발생하는 오버헤드를 분석한다.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10a
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• pp.334-336
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• 2003

본 논문에서는 차세대 인터넷 서버의 멀티미디어 파일 시스템인 Content Container파일 시스템(CCFS)의 로그 기반 회복 기법을 설계하고 구현한 내용에 대해 기술한다. CCFS에서는 트랜잭션들이 개별적으로 로깅 할 수 있도록 함으로써 동시성을 높이면서 트랜잭션 수행 중에 로깅으로 인한 오버헤드를 줄인다. 그리고 로그 파일을 순환 구조로 사용할 수 있도록 효율적인 관리를 제공한다. 또한 시스템 고장이 발생하였을 때 로그 파일을 한번만 스캔하면서 완료한 트랜잭션에 대한 로그를 재수행함으로써 시스템의 빠른 회복과 재시작을 보장한다.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04a
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• pp.413-415
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• 2003

일반 사용자는 침입이 있더라도 항상 신뢰성 있는 정보를 획득하길 원하기 때문에 침입에 의하여 파일이 훼손되는 경우에도 사용자에게 투명한 방법으로 복구할 수 있는 방법이 필요하다. 본 논문에서는 리눅스 기반의 파일 시스템에서 변경이 일어날 때마다 로그 형태로 저장한 중복 파일을 이용하여 침입에 의하여 훼손된 부분을 복구하기 위한 기법을 제안한다. 실제 파일 변경이 일어날 때에는 그 변경이 악의적인지 합법적인지 판단이 불가능하다는 점에서 변경이 일어날 때마다 로그 형태로 변경정보를 유지하고 복구가 필요할 경우 선택적으로 적용할 수 있도록 하였다. 또한 로그 크기의 계속적인 증가에 효과적으로 대처하기 위한 로그 컴팩션(compaction) 방법도 보인다.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10a
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• pp.637-639
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• 2004

인터넷의 확산으로 인한 바이러스의 감염, 정전 등의 재해로 인해 파일 시스템이 손상될 수 있기 때문에 이를 복구하기 위한 기법들에 대한 다양한 연구가 이루어지고 있다. 그러나 기존 연구들은 파일 시스템이 정상적으로 동작하는 환경에서 수행 도중의 오류를 복구하기 위한 로그 기법들이 주로 사용되고 있다. 이러한 기법들은 파일 시스템의 기본구조가 손상될 경우 해당 디스크에 접근이 불가능하기 때문에 한계점이 존재한다 따라서 본 논문에서는 파일 시스템 기본 구조 복구 모델을 제안한다. 또한 실수로 파일을 완전히 삭제할 경우 운영체제가 제공하는 정상적인 방법으로는 삭제된 파일에 접근 할 수 없다. 따라서 완전히 삭제된 파일을 복구할 수 있는 방안을 제시하고 이를 구현하였다.