Sungjin Lee

As flash memory technologies quickly improve, NAND flash memory-based storage devices are becoming a viable alternative as a secondary storage solution for general-purpose computing systems such as personal computers and enterprise server systems. Most existing flash translation layer (FTL) schemes are, however, ill-suited for such systems because they were optimized for storage write patterns of embedded systems only. In this paper, we propose a new flash management technique called LAST which

The multi-level cell (MLC) NAND flash memory technology enables multiple bits of information to be stored on a single cell, thus making it possible to increase the density of the memory without increasing the die size. For most MLC flash memories, each cell can be programmed as a single-level cell or a multi-level cell during runtime. Therefore, it has a potential to achieve both the high performance of SLC flash memory and the high capacity of MLC flash memory. In this paper, we present a fl

In flash storage, an FTL is a complex piece of code that resides completely inside the storage device and is provided by the manufacturer. Its principal virtue is providing interoperability with conventional HDDs. However, this virtue is also its biggest impediment in reaching the full performance of the underlying flash storage. We propose to refactor the flash storage architecture so that it relies on a new block I/O interface which does not permit overwriting of data without intervening erasu

The performance and lifetime of highperformance solid-state drives (SSDs) can be improved by data compression, which can reduce the amount of data physically transferred from/to flash memory. In this paper, we present our experience of building a high-performance solid-state drive using a hardware accelerated compression module called BlueZIP. In order to fully exploit the BlueZIP module, we devise a compression-aware flash translation layer (FTL), called CaFTL, which supports compressionaware a

International audience

A SCADA (Supervisory Control And Data Acquisition) system is an industrial control and monitoring system for national infrastructures. The SCADA systems were used in a closed environment without considering about security functionality in the past. As communication technology develops, they try to connect the SCADA systems to an open network. Therefore, the security of the SCADA systems has been an issue. The study of key management for SCADA system also has been performed. However, existing key

Convolutional Neural Network (CNN) has been used in a variety of fields such as computer vision, speech recognition, and natural language processing. Because the amount of computation has increased tremendously, CNN has lately been accelerated through accelerators such as Graphic Processing Unit (GPU). However, resource-constrained embedded platforms such as Internet of Things (IoT) devices cannot afford to have such accelerators. Therefore, it is important to accelerate CNN by only the CPU effi

The multi-level cell (MLC) NAND flash memory technology enables multiple bits of information to be stored in a memory cell, thus making it possible to increase the density of flash memory without increasing the die size. In MLC NAND flash memory, each memory cell can be programmed as a single-level cell or a multi-level cell at runtime because of its performance/capacity asymmetric programming property, which is called flexible programming in this paper. Therefore, MLC flash memory has a potenti

Flash storage devices behave quite differently from hard disk drives (HDDs); a page on flash has to be erased before it can be rewritten, and the erasure has to be performed on a block which consists of a large number of contiguous pages. It is also important to distribute writes evenly among flash blocks to avoid premature wearing. To achieve interoperability with existing blockI/O subsystems for HDDs, NAND flash devices employ an intermediate software layer, called the flash translation layer

NAND flash-based storage device is becoming a viable storage solution for mobile and desktop systems. Because of the erase-before-write nature, flash-based storage devices require garbage collection that causes significant performance degradation, incurring a large number of page migrations and block erasures. To improve I/O performance, therefore, it is important to develop an efficient garbage collection algorithm. In this paper, we propose a novel garbage collection technique, called buffer-a

As the cell size of NAND flash memory is shrinking, its physical characteristics such as performance and lifetime are significantly degraded. As effective solutions of overcoming such poor physical characteristics, more cross-layer system-level approaches (such as compression and deduplication techniques) are expected to be developed. These system-level techniques typically employ intelligent software algorithms supported by specialized hardware accelerators. Using hardware accelerators combined

NAND flash-based Solid-State Drives (SSDs) are becoming a viable alternative as a secondary storage solution for many computing systems. Since the physical characteristics of NAND flash memory are different from conventional Hard-Disk Drives (HDDs), flash-based SSDs usually employ an intermediate software layer, called a Flash Translation Layer (FTL). The FTL runs several firmware algorithms for logical-to-physical mapping, I/O interleaving, garbage collection, wear-leveling, and so on. These FT

As the semiconductor process is scaled down, the endurance of NAND flash memory greatly deteriorates. To overcome such a poor endurance characteristic and to provide a reasonable storage lifetime, system-level endurance enhancement techniques are rapidly adopted in recent NAND flash-based storage devices like solid-state drives (SSDs). In this paper, we propose an integrated lifetime management approach for SSDs. The proposed lifetime management technique combines several lifetime-enhancement sc

NAND flash memory is commonly known as a power-efficient storage medium. Because of the increasing complexity of flash-based storage devices, however, it is more difficult to achieve good power-efficiency without considering an energy-efficient storage device design. In this paper, we investigate the potential benefit of dynamic voltage/frequency scaling (DVFS) on the energy-efficiency of flash-based storage devices. We first develop a performance/power model for a flash device by using an FPGA-

As the semiconductor process is scaled down, the endurance of NAND flash memory greatly deteriorates. To overcome such a poor endurance characteristic and to provide a reasonable storage lifetime, system-level endurance enhancement techniques are rapidly adopted in recent NAND flash-based storage devices like solid-state drives (SSDs). In this paper, we propose an integrated lifetime management approach for SSDs. The proposed lifetime management technique combines several lifetime-enhancement sc