• Journal of KIISE:Computer Systems and Theory
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• v.35 no.2
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• pp.94-101
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• 2008

Non-volatile RAM (NVRAM) is a form of next-generation memory that has both characteristics of nonvolatility and byte addressability each of which can be found in nonvolatile storage and RAM, respectively. The advent of NVRAM may possibly bring about drastic changes to the system software landscape. When NVRAM is efficiently exploited in the system software layer, we expect that the system performance can be significantly improved. In this regards, we attempt to develop a new Flash file system, named MiNVFS (Metadata in NVram File System). MiNVFS maintains all the metadata in NVRAM, while storing all file data in Flash memory. In this paper, we present quantitative experimental results that show how much performance gains can be possible by exploiting NVRAM. Compared to YAFFS, a typical Flash file system, we show that MiNVFS requires only minimal time for mounting. MiNVFS outperforms YAFFS by an average of around 400% in terms of the total execution time for the realistic workloads that we considered.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.2
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• pp.241-245
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• 2008

Non-volatile RAM (NVRAM) has both characteristics of nonvolatility and byte addressability. In order to efficiently exploit this NVRAM in the file system layer, we proposed the MiNV (Metadata in NVram) file system in our previous research. MiNV file system maintains all the metadata in NVRAM while storing file data in NAND Flash memory. In this paper, we experimentally analyze the efficiency for the execution of garbage collection in the MiNV file system. Also, we quantify the file system performance gains obtained from efficient garbage collection. Experimental results show that garbage collection on the MiNV file system executes more efficiently that on YAFFS even though these file systems adopt exactly the same garbage collection policy. Specifically, the MiNV file system invokes the aggressive garbage collection mechanism less frequently than YAFFS. Additionally, the MiNV file system postpones the first execution of the aggressive garbage collection mechanism in our experiments. From the experiments, we verify that the efficiency of garbage collection leads to performance improvements of the MiNV file system.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.247-248
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• 2009

램 디스크는 주기억장치의 일부 영역을 스토리지로 이용하는 디스크 시스템이다. 램 디스크는 반도체 메모리에 데이터를 저장하고 접근하기 때문에 디스크 입출력 성능은 매우 높다. 그러나, 휘발성 메모리를 이용하는 램 디스크는 전원 공급이 중단되면 그 저장 내용이 소실되는 단점을 가지고 있다. 본 논문에서는 리눅스 장치 구동기 수준에서 램 디스크 서비스와 동시에 하드 디스크 등의 비휘발성 저장 장치에 데이터를 저장, 서비스하는 하이브리드 디스크 시스템을 제안한다.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10b
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• pp.199-201
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• 2004

모바일 장치에서 많이 사용되는 플래시 메모리는 작고, 저전력을 사용하며 내구성을 지니는 비휘발성 저장장치이다. 플래시 메모리의 읽기 속도는 램과 비슷하며, 대용량화 되어가고 있지만 쓰기 속도가 램에 비해 느리고, 블록에 대한 쓰기가 제한되어 있다. 현재의 디스크 기반의 DBMS 와는 달리 플래시 메모리용 저장장치를 설계함에 있어 트랜잭션 실패시의 회복기법이 같은 블록에 다시 쓰기가 불가능한 플래시 메모리의 특성을 고려하는 것이 중요하다. 본 연구에서 LFS에 Shadow Paging을 응용하여 플래시 메모리의 블록에 대한 쓰기 횟수를 줄이고 플래시 메모리의 특성에 맞추어 트랜잭션 실패시 효율적인 데이터 복구를 가능하게 하는 회복기법을 제안한다.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.3
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• pp.336-340
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• 2010

Flash storages are prevalent as portable storage in computing systems. When we consider the detachability of Flash storage devices, data integrity becomes an important issue. To assure extreme data integrity, file systems synchronously write all file data to storage accompanying hot write references. In this study, we concentrate on the effect of hot write references on Flash storage, and we consider the effect of absorbing the hot write references via nonvolatile write cache on the performance of the FTL schemes in Flash storage. In 80 doing, we quantify the performance of typical FTL schemes for workloads that contain hot write references through a wide range of experiments on a real system environment. Through the results, we conclude that the impact of the underlying FTL schemes on the performance of Flash storage is dramatically reduced by absorbing the hot write references via nonvolatile write cache.

• Proceedings of the Korean Information Science Society Conference
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• 2007.06a
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• pp.256-257
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• 2007

• Proceedings of the Korean Information Science Society Conference
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• 2007.10a
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• pp.237-238
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• 2007

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.5
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• pp.537-541
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• 2008

Log-Structured File System(LFS) is a disk based file system that is optimized for improving the write performance. LFS gathers dirty data in memory as long as possible, and flushes all dirty data sequentially at once. In a real system, however, maintaining dirty data in memory should be flushed into a disk to meet file system consistency issues even if more memory is still available. This synchronizations increase the cleaner overhead of LFS and make LFS to write down more metadata into a disk. In this paper, by adapting Non-volatile RAM(NV-RAM) we modifies LFS and virtual memory subsystem to guarantee that LFS could gather enough dirty data in the memory and reduce small disk writes. By doing so, we improves the performance of LFS by around 2.5 times than the original LFS.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.3
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• pp.171-180
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• 2009

Slowly, but surely, we are seeing the emergence of a variety of embedded systems that are employing Storage Class RAM (SCRAM) such as FeRAM, MRAM and PRAM, SCRAM not only has DRAM-characteristic, that is, random byte-unit access capability, but also Disk-characteristic, that is, non-volatility. In this paper, we propose a new software architecture that allows SCRAM to be used both for main memory and for secondary storage simultaneously- The proposed software architecture has two core modules, one is a SCRAM driver and the other is a SCRAM manager. The SCRAM driver takes care of SCRAM directly and exports low level interfaces required for upper layer software modules including traditional file systems, buddy systems and our SCRAM manager. The SCRAM manager treats file objects and memory objects as a single object and deals with them in a unified way so that they can be interchanged without copy overheads. Experiments conducted on real embedded board with FeRAM have shown that the SCRAM driver indeed supports both the traditional F AT file system and buddy system seamlessly. The results also have revealed that the SCRAM manager makes effective use of both characteristics of SCRAM and performs an order of magnitude better than the traditional file system and buddy system.

• Proceedings of the Korean Society of Computer Information Conference
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• 2017.07a
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• pp.3-4
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• 2017

DRAM, HDD의 성장세가 둔화되면서 NVM이 그 대안으로 떠오르고 있다. Xpoint, Z-SSD등 여러 고성능 NVM이 발표되고 있으며 DRAM의 성능을 목표로 하고 있다. 본 논문에서는 DRAM 수준의 고성능 NVM이 상용화 될 때 어느 정도의 성능과 가격지표를 보일 것이며 이에 대한 가격과 저장공간의 트레이드오프는 어느 정도일지 알아보기 위해 실험을 진행하였다. RAM disk로 NVM환경을 시뮬레이션 하였고 SSD, HDD 간 I/O 성능을 측정하였다. NVM과 SSD는 70배에서 200배, NVM과 디스크는 98배에서 3000배 이상 차이가 있음을 확인했다. 이 결과를 바탕으로 RAM disk와 SSD 가격지표를 조사하여 IOPS/$를 도출해 보았고 NVM이 7배의 IOPS/$를 가지지만 SSD가 18배의 GB/$를 가지는 것을 확인할 수 있었다.