P-BMS

Flash memory is a non-volatile storage device that can retain its contents when the power is switched off. Generally, it is a form of an electrically erasable programmable read-only memory (EEPROM) that offers several excellent features such as less noise, solid-state reliability, lower power consumption, smaller size, light weight, and higher shock resistant [1 – 5]. Flash memory acts as a slim and compact storage device. It’s main applications are such as compact flash (CF), secured digital (SD), and personal computer memory card international association (PCMCIA) cards, for storage and data transfer in most portable electronic gadgets such as mobile phones, digital cameras, personal digital assistants (PDAs), portable media players (PMPs), gobal positioning system receivers (GPS), just to name a few.

Flash memory is widely utilized for secondary storage today. However, its further use is hindered by the lifetime issue, which is mainly impacted by wear leveling and bad block management (BBM). Besides initial bad blocks resulting from the manufacturing process, good blocks may eventually wear out due to the limited write endurance of flash cells, even with the best wear leveling strategy. Current BBM tracks both types of bad blocks, and keeps them away from regular use. However, when the amount of bad blocks exceeds a threshold, the entire chip is rendered non-functional. In this paper, we reconsider existing BBM, and propose a novel one that reuses worn-out blocks, utilizing them in wear leveling. Experimental results show that compared to a state-of-the-art wear leveling algorithm, our design can reduce worn-out blocks by 46.5% on average with at most 1.2% performance penalties.

Recent consumer devices such as smartphones, smart TVs and tablet PCs adopt NAND flash memory as storage device due to its advantages of small size, reliability, low power consumption, and high performance. The unique characteristics of NAND flash memory require an additional software layer, called flash translation layer (FTL), between traditional file systems and flash memory. In order to reduce the garbage collection cost, FTLs generally try to separate hot and cold data. Previous hot and cold separation techniques monitor the storage access patterns within storage device, or exploit file system hints from host system. This paper proposes a novel clustered page-level mapping, called CPM, which can separate hot and cold data efficiently by allocating different flash memory block groups to different logical address regions. CPM can reduce the FTL map loading overhead during garbage collection and it does not require any high-cost monitoring overhead or host hint. This paper also proposes a K-associative version of CPM, called K-CPM, which allows different logical address regions to share a physical block group in order to achieve high block utilizations. Experimental results show that CPM improves the storage I/O performance by about 54% compared with a previous page-level mapping FTL, and K-CPM further improves the performance by about 19.4% compared with CPM.

Flash memory, especially NAND flash memory, is being rapidly deployed as data storage for mobile devices such as mobile phones, digital cameras and PDA's. With its capacity increasing and price dropping, Flash memory has been installed in many portable computers instead of magnetic disk for its light weight, small size, physical stability and low power consumption. We may expect that Flash memory will finally take the place of magnetic disk in the next few years. It is possible for us to consider running a database system on the flash computing platforms. Therefore, this requires an efficient index structure to locate a particular item quickly from a huge amount of database records. However, disk-based database index can not be used on flash memory directly because of different characteristics between flash memory and magnetic disk. In this paper, we propose a logging approach on B+-tree index for flash-based DBMS. This new approach makes use of the characteristics of flash memory effectively to acquire more benefits from using traditional database index technology on flash memory.

In recent years, flash memory has been widely used in embedded systems, portable devices, and high-performance storage products due to its non-volatility, shock resistance, low power consumption, and high performance natures. To reduce the product cost, multi-level-cell flash memory (MLC) has been proposed; compared with the traditional single-level-cell flash memory (SLC) that only stores one bit of data per cell, each MLC cell can store two or more bits of data. Thus MLC can achieve a larger capacity and reduce the cost per unit. However, MLC also suffers from the degradation in both performance and reliability. In this paper, we try to enhance the reliability and reduce the product cost of flash-memory based storage devices from a totally different perspective. We propose a half-level-cell (HLC) management scheme to manage and reuse the worn-out space in solid-state drives (SSDs); through our management scheme, the system can treat two corrupted pages as a normal page without sacrificing performance and reliability. To the best of our knowledge, this is the first research that reclaims free space by reviving the corrupted pages. The experiment results show that the lifetime of SSD can be extended by 48.54% for the trace of general users applications with our proposed HLC management scheme.

NAND flash memory has cost competitiveness, since the process technology which can store multi-bit in a cell is developed. Because of this technology, NAND flash memory is widely used for storage system of various electronic devices. Even though the capacity per unit area is consistently increased with the development of process technology, the cell-to-cell interference rises accordingly and it makes the possibility of bad block increase rapidly. In this paper, we analyzed the pattern of bad page by using the platform board, and we propose the lifetime enhancement scheme of flash storage system based on the experimental results.

With the rapid development of computer technology as a whole, the performance requirements of modern computer systems for storage technology are becoming higher and higher. This paper discusses the response to the problems that have arisen with the traditional storage in today's era, that is, the construction principle of the new storage three-dimensional memory (3D NAND) and the future development. Traditional storage in order to enhance the storage space of the plane flash memory, can only be components for shrinking, when shrinking to a certain extent when the flash memory will occur uncontrollable hidden danger, so the invention of 3D NAND. By vertically stacking many layers of memory cells, the storage density per unit area is greatly increased, with high-speed reading and writing, large capacity, low power consumption and other characteristics. Nowadays, 3D NAND is widely used in enterprises, and the industry is hopeful about the long-term prospects of the growing global demand for data generation and storage and the introduction of new technologies. The development of 3D NAND technology provides higher storage density and lower cost for NAND flash memory to meet the growing demand for data storage. This paper provides a systematic summary of existing research on 3D NAND in the hope that it will better enhance the overall technology improvement in the storage industry.

The flash memory becomes a very popular storage device. Recently, it has replaced the traditional hard disc due to its shock - resistance and low power consumption. However, the flash memory architecture has some limitations related to the data management. Data cannot be updated in-place. That is why the flash translation layer (FTL) must be used. Nowadays, the flash memory seems to be the mature enough storage technology to work with databases. Among many database models, the column oriented databases have attracted the attention. This approach indicates the fact that data from the columns are packed together in the memory blocks. In this paper, we propose the Column Flash Translation Layer (CFTL) as an effective tool to store the data of the column oriented database in blocks of the flash memory

There is no doubt that video-on-demand (VoD) services are very popular these days. However, disk storage is a serious bottleneck limiting the scalability of a VoD server. Disk throughput degrades dramatically due to seek time overhead when the server is called upon to serve a large number of simultaneous video streams. To address the performance problem of disk, buffer cache algorithms that utilize RAM have been proposed. Interval caching is a state-of-the-art caching algorithm for a VoD server. Flash Memory Solid-State Drive (SSD) is a relatively new storage technology. Its excellent random read performance, low power consumption, and sharply dropping cost per gigabyte are opening new opportunities to efficiently use the device for enterprise systems. On the other hand, it has deficiencies such as poor small random write performance and limited number of erase operations. In this paper, we analyze tradeoffs and potential impact that flash memory SSD can have for a VoD server. Performance of various commercially available flash memory SSD models is studied. We find that low-end flash memory SSD provides better performance than the high-end one while costing less than the high-end one when the I/O request size is large, which is typical for a VoD server. Because of the wear problem and asymmetric read/write performance of flash memory SSD, we claim that interval caching cannot be used with it. Instead, we propose using file-level Least Frequently Used (LFU) due to the highly skewed video access pattern of the VoD workload. We compare the performance of interval caching with RAM and file-level LFU with flash memory by simulation experiments. In addition, from the cost-effectiveness analysis of three different storage configurations, we find that flash memory with hard disk drive is the most cost-effective solution compared to DRAM with hard disk drive or hard disk drive only.

In recent years, flash memory has become more widely used due to its advantages, such as fast data access, low power consumption, and high mobility. However, flash memory also has drawbacks that need to be overcome, such as erase-before-write, and the limitations of block deletion. In order to address this issue, the FTL (Flash Translation Layer) has been proposed with useful functionalities like address mapping, garbage collection, and wear-leveling. During the process of using, the data may be lost on power failure in the storage systems. In some systems, the data is very important. Thus recovery of data in the event of the system crash or a sudden power outage is of prime importance. This problem has attracted attention from researchers and many studies have been done. In this paper, we investigate previous studies on data recovery for flash memory from FTL processing solutions to PLR (Power Loss Recovery) solutions that have been proposed by authors in the conference proceeding, patents, or professional journals. This will provide a discussion of the proposed solutions to the data recovery in flash memory as well as an overview.

A NAND flash SSD has been widely used as a storage device because of its fast access speed and low power consumption. It inherits distinctive features such as no in-place update because it consists of NAND flash arrays. When implementing a B-tree on flash SSDs, the performance degradation occurs due to intensive updates in the same node. In this paper, we propose a B-tree employing a cascade memory node on NAND flash SSDs in order to reduce intensive overwrites. Our B-tree keeps the modified data so as to delay write operations and performs the flushing of memory node in batch process. Through the experiment, we show the superiority of our B-tree compared to related techniques.

Flash memory is rapidly deployed as data storage for embedded and tablet PCs due to its shock resistance, fast access, and low power consumption. However, it has some intractable characteristics such as erase-before-write, asymmetric read/write/erase speed, and limited number of write/erase cycles. Due to these hardware limitations, the magnetic disk-based systems and applications could hardly make full use of the advantages of flash memory when directly adopting themselves on it. For example, the frequent changes of B-tree can degrade the storage performance of flash memory. Most of the recent studies on flash-aware index design focused mainly on the buffer management scheme whereby they can reduce the costly write operations to flash. However, in this paper, we present a novel B-tree storage scheme, a group round robin based B-tree index storage scheme, which applies a dynamic grouping and round robin techniques for erase-minimized storage of B-tree in flash memory under heavy-update workload. Experiment results show that the proposed scheme is efficient for frequently changed B-tree structure and improves the I/O performance by 2.14X at best, compared to the related work.

Recently, NAND flash memory has emerged as a next generation storage device because it has several advantages, such as low power consumption, shock resistance, and so on. However, it is necessary to use a flash translation layer (FTL) to intermediate between NAND flash memory and conventional file systems because of the unique hardware characteristics of flash memory. This paper proposes a new clustered FTL (CFTL) that uses clustered hash tables and a two-level software cache technique. The CFTL can anticipate consecutive addresses from the host because the clustered hash table uses the locality of reference in a large address space. It also adaptively switches logical addresses to physical addresses in the flash memory by using block mapping, page mapping, and a two-level software cache technique. Furthermore, anticipatory I/O management using continuity counters and a prefetch scheme enables fast address translation. Experimental results show that the proposed address translation mechanism for CFTL provides better performance in address translation and memory space usage than the well-known NAND FTL (NFTL) and adaptive FTL (AFTL).

Flash memory has been widely used in various embedded computing systems and portable devices in recent years because of its small size, shock-resistance, low-power consumption and non-volatile properties. To hide the disadvantages of flash memory such as out-of-place update, a flash translation layer (FTL) is usually used for providing transparent block-device emulation. But when index structures are implemented over FTL, intensive overwrite operations caused by record inserting, deleting, modifying and index reorganizing could not only degrade the performance significantly but also reduce the life of flash memory. To address the problem, BFTL and IBSF are proposed. However, neither of them could avoid the loss of records and incompatibilities when system crash occurs. In this paper, a reliable B-tree implementation called RBFTL is presented for flash-memory storage systems. It is placed between the application layer and FTL. RBFTL could minimize the loss of data and eliminate incompatibilities effectively and efficiently when system crashes. The experimental results also show that RBFTL yields a better performance than FTL.

Databases are more and more used in embedded system applications and especially in consumer electronics. This comes from the need to structure user and/or system data to be more efficiently managed and accessed. The transactional database management systems widely used in embedded systems have been designed considering hard disk drives as the storage device. In embedded systems, NAND flash memory is the main storage media and its intricacies make it fundamentally different from hard drives on many points of view, in particular in terms of performance and access mode. The performance behavior of on-flash database applications remains largely unknown, and we believe a better adequacy between those applications and flash management systems would lead to strong optimizations. A first step in that process is to assess and understand the performance behavior of database applications on flash memory. For this sake, this paper presents a micro benchmarking and modeling methodology, as well as the associated results and analysis for SQLite database queries on embedded flash specific file systems. SQLite is one of the most used database application in embedded systems and especially consumer electronics. This methodology has been applied and validated on two embedded hardware platforms. Flash file systems (FFS) behavior are very specific to flash memory intricacies and the objective of this study is to highlight the interactions between flash memory, FFSs, and SQLite based applications. The model proved to be very accurate in predicting flash I/O performance for a given workload.