• KIPS Transactions on Computer and Communication Systems
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• v.12 no.1
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• pp.1-8
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• 2023

It is impossible to overwrite on an already allocated page in SSDs, so whenever a write operation occurs a page replacement with a clean page is required. To resolve this problem, SSDs have an internal flash translation layer called FTL that maps logical pages managed by a file system of operating system to currently allocated physical pages. SSD pages discarded due to write operations must be recycled through initialization, but since the number of initialization times is limited the FTL provides a caching function to reduce the number of writes in addition to the page mapping function, which is a core function. In this study, we focus on the FTL cache methodologies reducing the number of page writes and analyze the related algorithms, and propose a write-only cache strategy. As a result of experimenting with the write-only cache using a simulator, it showed an improvement of up to 29%.

• International journal of advanced smart convergence
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• v.9 no.3
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• pp.253-259
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• 2020

Most of today's large-scale cloud systems and enterprise data centers are distributing resources to improve scalability and resource utilization. NVMe-over-Fabric protocol allows submitting NVMe commands to a remote NVMe SSD through RDMA (Remote Direct Memory Access) network. It is attracting attention recently because it is possible to construct a disaggregation storage system with low latency through the protocol. However, the current I/O stack of NVMe-over-Fabric has an inefficient structure for maintaining compatibility with the traditional I/O stack. Therefore, in this paper, we propose a new mechanism to reduce I/O latency and CPU overhead by modifying I/O path of NVMe-over-Fabric to pass through legacy block layer. According to the performance evaluation results, the proposed mechanism is able to reduce the I/O latency and CPU overhead by up to 22% and 24% compared to the existing NVMe-over-Fabrics protocol, respectively.

• Journal of the Korea Society of Computer and Information
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• v.22 no.12
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• pp.9-15
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• 2017

This paper presents an efficient FTL for NAND flash based SSDs. Address translation information of page mapping based FTLs is stored on flash memory pages and address translation cache keeps frequently accessed entries. The proposed FTL of this paper reduces response time by considering both of temporal and spacial localities of page access patterns in translation cache management. The localities of several well-known traces are evaluated and determine the structure of the cache for high hit ratio. A simulation with several well-known traces shows that the presented FTL reduces response time in comparison to previous FTLs and can be used with relatively small size of caches.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06c
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• pp.206-209
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• 2011

오래전부터 바이오 정보 처리에 대한 관심은 매우 높았으며, 컴퓨터의 성능 발달에 따라 기존에 처리할 수 없었던 대용량 바이오 데이터의 처리가 가능해 지면서 바이오 컴퓨팅의 역할이 점차 커지고 있다. 보다 효과적인 바이오 컴퓨팅을 위해서는 빠른 데이터 처리 속도가 필수적이며 이를 위하여 근본적으로 컴퓨터의 데이터 처리 성능을 향상시킬 필요가 있다. 본 논문에서는 최근에 각광받고 있는 SSD와 멀티코어 시스템을 이용하여 컴퓨터의 성능을 올려 대표적인 바이오 데이터의 처리 도구인 BLAST에 얼마나 효과적인지를 실험을 통하여 검증하고 그 가능성을 분석하였다. 또한 SSD에서의 바이오 데이터 최적화를 위하여 필요한 정보를 수집하고 사용 방안을 모색해보았다.

• Transactions of the Society of Information Storage Systems
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• v.6 no.2
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• pp.41-46
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• 2010

Recently, Flash Memory Drives are one of the best media to support portable and desktop computers' storage devices. Their features include non-volatility, low power consumption, and fast access time for read operations, which are sufficient to present flash memories as major database storage components for desktop and server computers. However, we need to improve traditional storage management schemes based on HDD(Hard Disk Drive) and RAID(Redundant Array of Independent Disks) due to the relatively slow or freezing characteristics of write operations of SSDs, as compared to fast read operations. In order to achieve this goal, we propose a new storage management scheme called Hetero-Mirroring based on traditional HDD mirroring scheme. Hetero-Mirroring-based storage management improves RAID-1 operation performance by balancing write-workloads and delaying write operations to avoid SSD freezing.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.1121-1124
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• 2012

열-지향 데이터베이스 시스템인 C-Store는 많은 상용 데이터베이스 시스템과는 달리 데이터를 행(row) 위주가 아닌 열(column) 위주로 저장을 하여, 데이터 웨어하우스와 같이 주로 읽기 IO를 유발하는 환경에서 데이터의 전송량을 줄임으로써, 높은 성능을 보였다. 본 논문에서는 대표적인 열 지향 저장 DBMS인 C-Store와 행 위주의 저장구조를 사용하는 기존 DBMS와의 차이점을 알아보고, C-Store의 저장장치로 하드디스크와 차세대 저장장치로 주목받고 있는 플래시 SSD(Solid State Disk)를 사용하였을 때, 발생할 수 있는 장단점에 대해 분석하였다.

• IEMEK Journal of Embedded Systems and Applications
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• v.14 no.2
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• pp.63-69
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• 2019

Recently, ultra-low latency flash storage devices such as Z-SSD and Optane SSD were introduced with the significant technological improvement in the storage devices which provide much faster response time than today's other NVMe SSDs. With such ultra-low latency, $10{\mu}s$, storage devices the cost of context switch could be an overhead during interrupt-driven I/O completion process. As an interrupt-driven I/O completion process could bring an interrupt handling overhead, polling or hybrid-polling for the I/O completion is known to perform better. In this paper, we analyze tail latency problem in a polling process caused by process scheduling in data center environment where multiple applications run simultaneously under one system and we introduce our adaptive polling selection technique which dynamically selects efficient processing method between two techniques according to the system's conditions.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.11a
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• pp.828-831
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• 2008

플래시 메모리(Flash Memory) 기술이 빠르게 발전하면서, 플래시 메모리 기반의 저장 장치가 개인용 컴퓨터나 엔터프라이즈 서버 시스템과 같은 시스템에 2차적인 저장 장치로써 사용가능해지고 있다. FTL(Flash Translation Layer)의 기본적인 기능은 플래시 메모리의 논리 주소를 물리 주소로 바꾸는 것임에도 불구하고, FTL의 효율적인 알고리즘은 성능과 수명에 상당한 효과를 가지고 있다. 이 논문에서는 MP3 플레이어와 디지털 카메라, SSDs(Solid-State Disk)와 같은 낸드 플래시 메모리(NAND Flash Memory) 기반의 어플리케이션을 위한 N : N+K 매핑을 사용하는 새로운 FTL 설계를 제안한다. 성능에 영향을 미치는 매개변수들을 분류하여, 다양한 워크로드 분석을 기반으로 FTL을 조사했다. 우리가 제안하는 FTL을 가지고, 낸드 플래시 어플리케이션 가동에 따라 어떤 매개변수가 최대 성능을 낼 수 있는지 알아낼 수 있고, 그 변수들을 유연하게 조정하여 성능을 더 향상시킬 수 있다.

• The KIPS Transactions:PartA
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• v.18A no.4
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• pp.135-142
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• 2011

This research is to design an effective buffer structure and its management for flash memory based high performance SSDs (Solid State Disks). Specifically conventional SSDs tend to show asymmetrical performance in read and /write operations, in addition to a limited number of erase operations. To minimize the number of erase operations and write latency, the degree of interleaving levels over multiple flash memory chips should be maximized. Thus, to increase the interleaving effect, an effective buffer structure is proposed for the SSD with a hybrid address mapping scheme and super-block management. The proposed buffer operation is designed to provide performance improvement and enhanced flash memory life cycle. Also its management is based on a new selection scheme to determine random and sequential accesses, depending on execution characteristics, and a method to enhance the size of sequential access unit by aggressive merging. Experiments show that a newly developed mapping table under the MBA is more efficient than the basic simple management in terms of maintenance and performance. The overall performance is increased by around 35% in comparison with the basic simple management.

• The KIPS Transactions:PartD
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• v.18D no.3
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• pp.157-168
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• 2011

Recently flash memory has been being utilized as a main storage device in mobile devices, and flashSSDs are getting popularity as a major storage device in laptop and desktop computers, and even in enterprise-level server machines. Unlike HDDs, on flash memory, the overwrite operation is not able to be performed unless it is preceded by the erase operation to the same block. To address this, FTL(Flash memory Translation Layer) is employed on flash memory. Even though the modified data block is overwritten to the same logical address, FTL writes the updated data block to the different physical address from the previous one, mapping the logical address to the new physical address. This enables flash memory to avoid the high block-erase cost. A flashSSD has an array of NAND flash memory packages so it can access one or more flash memory packages in parallel at once. To take advantage of the internal parallelism of flashSSDs, it is beneficial for DBMSs to request I/O operations on sequential logical addresses. However, the B-tree structure, which is a representative index scheme of current relational DBMSs, produces excessive I/O operations in random order when its node structures are updated. Therefore, the original b-tree is not favorable to SSD. In this paper, we propose AS(Always Sequential) B-tree that writes the updated node contiguously to the previously written node in the logical address for every update operation. In the experiments, AS B-tree enhanced 21% of B-tree's insertion performance.