• Journal of Digital Contents Society
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• v.14 no.2
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• pp.247-254
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• 2013

Storage Class Memory(SCM), such as PRAM, FRAM and MRAM, are expected to be comparable to DRAM in terms of access speed and to Flash memory in terms of capacity in a near future. In this paper, assuming that not only the secondary storage (HDD or Flash memory) but also the primary memory (DRAM) will be replaced by SCM in the future computer systems, we propose an efficient file access framework for the SCM based computer systems. The proposed framework do not assign exclusive area in the SCM to the file system and uses various memory-related techniques, such as unified data access path, zero-copy data read using file mapping, copy-on-write, and multiple page pre-faulting for file management. Based on the preliminary experimental results, we could conclude that the proposed framework can be an efficient baseline for designing a new operating system for the SCM based computer systems.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.2
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• pp.207-211
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• 2010

Storage Class Memory (SCM) has both characteristics of non-volatility and random byte addressability. The advent of SCM can bring about novel and innovative features that are not possible in con ventional computing systems. This paper suggests a new system design that turns on/off a system instantly. To do this, we replace the main memory with SCM to retain the volatile system states as the system is turned off. We implement our prototype in an embedded environment and measure its system on/off time.

• Journal of KIISE
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• v.42 no.1
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• pp.7-14
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• 2015

Storage Class Memory(SCM) has been considered as a next-generation storage device because it has positive advantages to be used both as a memory and storage. However, there are significant problems of data consistency in recently proposed file systems for SCM such as insufficient data consistency or excessive data consistency-control overhead. This paper proposes a novel data consistency-control scheme, which changes the write mode for log data depending on the modified data ratio in a block, using a rollback-recovery scheme instead of the Write Ahead Logging (WAL) scheme. The proposed scheme reduces the log data size and the synchronization cost for data consistency. In order to evaluate the proposed scheme, we implemented our scheme on a Linux 3.10.2-based system and measured its performance. The experimental results show that our scheme enhances the write throughput by 9 times on average when compared to the legacy data consistency control scheme.

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.1
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• pp.19-26
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• 2010

In this paper, we adopt Storage Class Memory, which is next-generation non-volatile RAM technology, as part of main memory parallel to DRAM, and exploit the SCM+DRAM main memory system from the dependability perspective. Our system provides instant system on/off without bootstrapping, dynamic selection of process persistence or non-persistence, and fast recovery from power and/or software failure. The advantages of our system are that it does not cause the problems of checkpointing, i.e., heavy overhead and recovery delay. Furthermore, as the system enables full application transparency, our system is easily applicable to real-world environments. As proof of the concept, we implemented a system based on a commodity Linux kernel 2.6.21 operating system. We verify that the persistence enabled processes continue to execute instantly at system off-on without any state and/or data loss. Therefore, we conclude that our system can improve availability and reliability.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.547-555
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• 2023

High-density crossbar arrays based on storage class memory (SCM) are ideally suited to handle an exponential increase in data storage and processing as a central hardware unit in the era of AI-based technologies. To achieve this, selector devices are required to be co-integrated with SCM to address the sneak-path current issue that indispensably arises in such crossbar-type architecture. In this perspective, we first summarize the current state of tellurium-based threshold-switching devices and recent advances in the material, processing, and device aspects. We thoroughly review the physicochemical properties of elemental tellurium (Te) and representative binary tellurides, their tailored deposition techniques, and operating mechanisms when implemented in two-terminal threshold switching devices. Lastly, we discuss the promising research direction of Te-based selectors and possible issues that need to be considered in advance.

• Communications of the Korean Institute of Information Scientists and Engineers
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• v.27 no.5
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• pp.18-28
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• 2009

• The Journal of Korean Institute of Next Generation Computing
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• v.14 no.5
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• pp.40-52
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• 2018

Solid state drive (SSD) cache technologies that are used as a second-tier cache between the main memory and hard disk drive (HDD) have been widely studied. The SSD cache requires a new prefetching scheme as well as cache replacement algorithms. This paper presents a prefetching scheme for a storage-class cache using SSD. This prefetching scheme is designed for the storage-class cache and based on a long-term scheduling in contrast to the short-term prefetching in the main memory. Traditional prefetching algorithms just consider only read, but the presented prefetching scheme considers both read and write. An experimental evaluation shows 2.3% to 17.8% of hit rate with a 64GB of SSD and the 4GiB of prefetching size using an I/O trace of 14 days. The proposed prefetching scheme showed significant improvement of cache hit rate and can be easily implemented in storage-class cache systems.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.330.1-330.1
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• 2014

개인용 노트북, 태블릿 PC, 핸드폰 기술 발전에 의해 언제 어디서나 데이터를 작성하고 기록하는 일들이 가능해졌다. 특히 cloud 시스템을 이용하여 데이터를 휴대기기에 직접 저장하지 않고 server에 기록하는 일들이 가능해짐에 따라 server 기기의 성능, server-room power 및 space 에 대한 관심이 증가하였다. Storage class memory (SCM) 이란 memory device와 storage device의 장점을 결합한 memory를 일컫는 기술로 현재 소형 디바이스 부분부터 점차 그 영역을 넓히고 있다. 그중 phase change material을 이용한 phase change memory (PCM) 기술이 가장 각광받고 있다. PCM의 경우 scaling됨에 의해 cell간의 열 간섭으로 인한 data 손실의 우려가 있어 cell의 면적을 최소화 하여 소자를 제작하여야 한다. 기존의 sputtering등의 PVD 방법으로는 한계가 있어 ALD 공정을 이용한 PCM에 대한 연구가 활발히 진행중이다. 특히 tellurium 원료기체로 silyl 화합물 [1]을 사용하여 주로 $Ge_2Sb_2Te_5$의 조성에 초점을 맞춰 진행되고 있으나, 세부 공정에 대한 기본적인 연구는 미비하다. 본 연구에서는 Ge-Sb-Te 3원계 박막을 형성하기 위한 Sb-Te 화합물의 증착 공정에 대한 연구를 수행하였다. 특히 원료기체로 Si이 없는 새로운 Te 원료기체를 이용하여 조성 조절을 하였고, 박막의 물성을 분석하였다. 또한 공정온도에 따른 박막의 물성 변화를 분석하였다.

• 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.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.2
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• pp.247-251
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• 2010

Using SCM in storage systems introduce new potentials for improving I/O performance and reliability. In this paper, we study the use of SCM as a buffer cache that guarantees transactional unit writes. Our proposed method can improve storage system reliability and performance at the same time and can recover the storage system immediately upon a system crash. The Proposed method is based on the LINUX JBD(Journaling Block Device), thus reliability is equivalent to JBD. In our experiments, the file system that adopts our method shows better I/O performance even while guaranteeing high reliability and shows fast file system recovery time (about 0.2 seconds).