• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.9
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• pp.54-62
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• 2015

Although NAND flash-based SSD (Solid-State Drive) provides superior performance in comparison to HDD (Hard Disk Drive), it has a major drawback in write endurance. As a result, the lifetime of SSD is determined by the workload and thus it becomes a big challenge in current technology trend of such as the shifting from SLC (Single Level Cell) to MLC (Multi Level cell) and even TLC (Triple Level Cell). Most previous studies have dealt with wear-leveling or improving SSD lifetime regarding hardware architecture. In this paper, we propose the optimal configuration of host I/O stack focusing on file system, I/O scheduler, and link power management using JEDEC enterprise workloads in terms of WAF (Write Amplification Factor) which represents the efficiency perspective of SSD life time especially for host write processing into flash memory. Experimental analysis shows that the optimum configuration of I/O stack for the perspective of SSD lifetime is MinPower-Dead-XFS which prolongs the lifetime of SSD approximately 2.6 times in comparison with MaxPower-Cfq-Ext4, the best performance combination. Though the performance was reduced by 13%, this contributions demonstrates a considerable aspect of SSD lifetime in relation to I/O stack optimization.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.48 no.5
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• pp.74-82
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• 2011

SSD has a limitation of number of erase/write cycles and does not allow in-place update unlike the hard disk because SSD is composed of an array of NAND flash memory. Thus, FTL is used to effectively manage SSD of having different characteristics from traditional disk. FTL has page, block, log-block mapping method. Among then, when log-block mapping method such as BAST and FAST is used, the performance of SSD is degraded because frequent merge operations cause lots of pages to be copied and deleted. This paper proposes a data allocation and replacement method based on access frequency by allocating PRAM as checking area of access frequency, log blocks, storing region of hot data in SSD. The proposed method can enhance the performance and lifetime of SSD by storing cold data to flash memory and storing log blocks and frequently accessed data to PRAM and then reducing merge and erase operations. Besides, a data replacement method is used to increase utilization of PRAM which has limitation of capacity. The experimental results show that the ratio of erase operations of the proposed method is 46%, 38% smaller than those of BAST and FAST and the write performance of the proposed method is 34%, 19% higher than those of BAST and FAST, and the read performance of the proposed method is 5%, 3% higher than those of BAST and FAST, respectively.

• KIISE Transactions on Computing Practices
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• v.24 no.3
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• pp.129-137
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• 2018

NVMe(Non-Volatile Memory Express) SSD(Solid State Drive) is a high-performance storage that makes use of flash memory as a storage cell, PCIe as an interface and NVMe as a protocol on the interface. It supports multiple I/O queues which makes it feasible to process parallel-I/Os on multi-core environments and to provide higher bandwidth than SATA SSDs. Hence, NVMe SSD is considered as a next generation-storage for data-center and cloud computing system. However, in the virtualization system, the performance of NVMe SSD is not fully utilized due to the bottleneck of the software I/O stack. Especially, when it uses I/O stack of the hypervisor or the host operating system like Xen and KVM, I/O performance degrades seriously due to doubled-I/O stack between host and virtual machine. In this paper, we propose a new I/O engine, called Direct-AIO (Direct-Asynchronous I/O) engine, that can access NVMe SSD directly for I/O performance improvements on QEMU emulator. We develop our proposed I/O engine and analyze I/O performance differences between the existed I/O engine and Direct-AIO engine.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.7
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• pp.57-64
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• 2011

To adjust the difference of bandwidth between host interface and NAND flash memory, DRAM is adopted as the buffer management in SSD (Solid-state Disk). In this paper, we propose cost-effective techniques to enhance SSD performance instead of using expensive high bandwidth DRAM. The SSD data can be classified into three groups such as user data, meta data for handling user data, and FEC(Forward Error Correction) parity/ CRC(Cyclic Redundancy Check) for error control. In order to improve the performance by considering the features of each data, we devise a flexible burst control method through monitoring system and a page based FEC parity/CRC application. Experimental results show that proposed methods enhance the SSD performance up to 25.9% with a negligible 0.07% increase in chip size.

• KIISE Transactions on Computing Practices
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• v.21 no.1
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• pp.52-57
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• 2015

In this paper, we analyze the performance of the TRIM commands on various SSDs and, based on our analysis results, we enhance the performance of these TRIM commands in the Ext4 file system. We observed that the performance of the TRIM commands improves as the size of the LBA-range increases, the sector number is aligned and continuous or more LBA-ranges are notified via a single TRIM command. However, although the performance is better when multiple LBA-ranges are informed by a single TRIM command, the Ext4 file system issues a single TRIM command for every LBA-range. In this paper, we modify the Ext4 file system to convey at most 64 LBA-ranges per TRIM command. Evaluations through Filebench show that the performance of file deletion operations is improved by up to 35%.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.4
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• pp.35-39
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• 2019

The shielding effectiveness (SE) of the EMI spray coating film was measured in a three-dimensional structure. The shielding effectiveness was measured by AST D4935 using coaxial type TEM cell. A standard sample of the cylindrical slab is fabricated to measure the shielding effectiveness using the ASTM D4935. At this time, spray coating was performed by bonding a three-dimensional structure with NAND flash memory to a standard sample. In the case of spray coating, it was uniformly coated not only on the horizontal plane but also on the vertical plane of the three-dimensional structure. As a result of measurement, shielding effectiveness of maximum 59 dB was measured in a three-dimensional structure similar to the case without three-dimensional structure. As a result, it was confirmed that the spray coating can be uniformed even in the three-dimensional structure.

• KIPS Transactions on Computer and Communication Systems
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• v.1 no.2
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• pp.71-78
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• 2012

The digital tachograph is a device that automatically records speed and distance of a vehicle, together with the driver's activity and vehicle status at an accident. It records vehicle speed, break status, acceleration, engine RPM, longitude and latitude of GPS, accumulated distance, and so on. European Commission regulation made digital tachographs mandatory for all trucks from 2005. Republic of Korea made digital tachographs mandatory for all new business vehicles from 2011 and is widening the range of vehicles that must install digital tachographs year by year. This device is used to analyze driver's daily driving information and car accidents. Under a car accident that makes the device reliability unpredictable, it is very important to store driving information with maximum reliability for its original mission. We designed and implemented a practical digital tachograph. This paper presents a storage scheme that consists of a first storage device with small capacity at a high reliability and a second storage device with large capacity at a low cost in order to reliably records data with a hardware at a low cost. The first storage device records data in a SLC NAND flash memory in a log-structured style. We present a reverse partial scan that overcomes the slow scan time of log-structured storages at the boot stage. The scheme reduced the scan time of the first storage device by 1/50. In addition, our design includes a scheme that fast stores data at a moment of accident by 1/20 of data transfer time of a normal method.