Empirical analysis of Android storage management using Network Block Device (NBD) protocol: A comprehensive performance and efficiency study

This paper describes a design and implementation of GNBD/VIA, a network block device (NBD) over virtual interface architecture (VIA), and evaluates its performance on Linux-based cluster of PCs. VIA is a user-level memory-mapped communication model which provides zero-copy communication by removing the operating system from the critical communication path. Typically, an NBD layer offers the abstraction of a storage media across the network. GNBD/VIA attempts to improve the performance of the NBD layer by employing the lightweight VIA communication mechanisms between NBD servers and clients. To our best knowledge, GNBD/VIA is the first implementation of NBD on VIA. GNBD/VIA outperforms the normal NBD placed on top of TCP/IP protocol stacks, and achieves the performance comparable to local disk devices, showing the read (write) bandwidth of 30.6MB/s (25.9MB/s) on the evaluation platform with UDM.9100 hard disks and Emulex cLAN adapters.

We propose a post-copy hot cloning mechanism to reduce service downtime of physical to virtual (P2V) migration. The conventional P2V migration requires to copy disk images from a physical to a virtual machine with stopping the system to ensure the consistency of the disk images, but it usually takes long time (e.g., several hours) because of slow I/O performance of storage devices. The proposed hot cloning mechanism copies disk images from a physical machine to a virtual machine in the background with running the system on the virtual machine. Since the disk image copy is the bottleneck of P2V migration, this hot cloning mechanism drastically reduces the service downtime. To ensure the consistency of disk images during the hot cloning, the hot cloning mechanism provides a block device of the source physical machine and a disk image (or block device) of the destination virtual machine as one virtualized block device that manages all I/O operations to the virtual machine. In this paper, we implement this post-copy hot cloning mechanism using the Linux Network Block Device (NBD) kernel module to support Linux-based hyper visors such as Xen and Linux KVM. We discuss the service downtime that is reduced by the proposed mechanism, and demonstrate that the implementation performs well in practical environments throughout the performance evaluations on the copy speed, hyper visor load, and system performance on a virtual machine.

Relaying systems, such as amplify-and-forward (AF), decode-and-forward (DF), selective DF (SDF) and incremental DF (IDF) relaying are usually used to ensure high performance and reliability for communication systems. A comprehensive energy efficiency performance study for different half-duplex relaying protocols, namely DF, SDF and IDF over visible light communication (VLC) channels is provided in this paper. Accurate analytical expressions for both outage probability and the minimum energy-per-bit performance of the aforementioned relaying systems are derived. For the sake of comparison and to justify the use of relays in the proposed system, the performance of a single-hop scenario is analyzed and compared to the relay-based links. The accuracy of the analysis is verified by Monte Carlo simulations. The results reveal that the single-hop VLC system offers the poorest performance compared to that offered by VLC relay-based systems particularly for relatively high end-to-end distances. However, the best performance is offered by SDF and IDF schemes as they have a lower outage probability than other systems under consideration. This work also shows that the performance of the systems under consideration is affected by some parameters, such as the vertical distance to user plane and the maximum cell radius of the LED.

A follow-up study to the U.S Department of Housing and Urban Development Lead-based Paint Abatement Demonstration Study (HUD DEMO)[1], the Comprehensive Abatement Performance Study (CAPS or CAP Study) [2], was performed by the U.S Environmental Protection Agency (EPA) to investigate the long-term efficacy of the abatement methods used during the HUD DEMO. This investigation included collection of approximately 30 dust and soil samples at each of 52 HUD DEMO houses in Denver. These samples were analyzed for lead content and evaluated by statistical analysis to address questions related to long-term efficacy of the abatement methods. This paper describes the sampling and analysis methods used during the CAP Study. Performance of the methods as determined by results from Quality Control (QC) samples originating from the field, laboratory sample preparation, and laboratory instrumental analysis are discussed. Variability of field sampling is found to be much higher than variability of laboratory processing.

In 1989 the U.S. Department of Housing and Urban Development (HUD) initiated the Lead-Based Paint Abatement Demonstration Study in seven urban areas across the U.S. in order to assess the cost, worker hazards, and short-term efficacy of various lead-based paint abatement methods. One question which was not answered by the HUD Abatement Demonstration was that of the long-term efficacy of the abatement methods. Therefore, in 1990 the U.S. Environmental Protection Agency (EPA) initiated the Comprehensive Abatement Performance (CAP) Study to address this question. This paper presents conclusions from the CAP Study regarding the efficacy of the HUD Demonstration abatement procedures, as well as results concerning the correlations among lead levels observed in dust and soil at various household locations.

The Comprehensive Abatement Performance (CAP) Study [1] was a U.S. Environmental Protection Agency (EPA) project designed to follow up on the FHA Lead-Based Paint Abatement Demonstration [2] conducted by the U.S. Department of Housing and Urban Development (HUD). The primary objective of the CAP Study was to assess the long-term efficacy of the various abatement methods employed during the HUD Demonstration. To address this objective, the U.S. EPA collected dust and soil samples at each of the 52 HUD Demonstration houses in Denver, Colorado, approximately two years after the abatements had been completed. This paper is the first in a series of three papers [3], [4] describing the CAP study. We present the experimental design employed to collect data in the study, provide a characterization of lead levels in dust and soil at these houses two years after abatement, and, finally, compare these levels with those in other abatement efficacy studies.

The present paper shows a performance test we have done to study the viability of a solution to build storage clouds using NBD (Network Block Device) and RAID technologies. This solution can be used both by providers and consumers of cloud storage services to exploit their distributed features, building and consuming high-capacity and fault-tolerant distributed storage systems.

Remote replication, also called remote mirror, is the key technology for data disaster tolerance. Replication system can be divided into synchronous and asynchronous mode according to whether the reply from remote server is required. In this paper, a remote replication system based on LVM (Logical Volume Manager) and NBD (Network Block Device) is presented in terms of the user requirements and Linux characteristic. Experimental results show that the system performance is acceptable both on LAN and WAN.

The cost of a conventional centralized file server, suitable for use in a learning environment such as a school, is high. However, in PC labs, there are normally several hundreds PCs, with plenty of free disk space. The total size of the unused capacity of the HDDs is almost equivalent to the capacity of a file server. In this paper, we propose constructing a virtual large-scale storage system by concatenating free disk space. We develop the VLSD (virtual large-scale disk) toolkit to aid the construction of such a system. This toolkit is implemented in Java and consists of RAID (redundant arrays of inexpensive/independent disks) and NBDs (network block device). In this paper, we describe how to use VLSD to implement a large-scale storage system.

There are many PCs in a PC room. For example, there are 500 PCs in our University. Each PC has a HDD, which is typically not full. If the disk utilization is 50% and each PC has a 240GB HDD, there is 60TB (500×120GB) free disk space. The total size of the unused capacity of these HDDs is nearly equal to the capacity of a file server. Institutions, however, tend to buy expensive appliance file servers. In this paper, we propose an efficient large-scale storage system that combines client free disk space. We have developed a java-based toolkit to construct a virtual large-scale storage system, which we call VLSD (Virtual Large-scale Disk). This toolkit is implemented in Java and consists of RAID (Redundant Arrays of Inexpensive/Independent Disks) and NBDs (Network Block Device). Using VLSD, we show how to construct a large disk that consists of multiple free spaces distributed over networks. VLSD supports typical RAID and other utility classes. These can be combined freely with one another.

The cost of a conventional centralized file server is high; though such a system is suited for a learning environment such as in schools. However, our university has several hundreds PCs whose HDDs are not usually used. The total size of these unused capacities of the HDDs is nearly equal to the capacity of a file server. Thus, in this paper, we propose a Java-based toolkit to construct a virtual large-scale storage system. We call it VLSD (virtual large-scale disk). This toolkit is implemented by Java and consists of RAID (redundant arrays of inexpensive/independent disks) and NBD (network block device). Using VLSD, we show how to construct a large disk that consists of multiple idle spaces distributed in networks. VLSD supports typical RAID classes and other utility classes. These can be combined freely with each other.

Comprehensive performance study on reflux solar methanol steam reforming reactor for hydrogen production

The objective of this study was to establish basic reading performance that could lead to useful design recommendations for print display text formats and layouts for the improvement of reading and comprehension performance of print text, such as academic writings, books, and newspapers, of Arabic language. Readability of English print text has been shown to be influenced by a number of typographical variables, including interline spacing, column setting and line length, and so on.Therefore, it is very important to improve the reading efficiency and satisfaction of print text reading and comprehension by following simple design guidelines. Most existing research on readability of print text is oriented to build guidelines for designing English texts rather than Arabic. However, guidelines built for English script cannot be simply applied for Arabic script because of orthographic differences. In the current study, manipulating interline spacing and column setting and line length generated nine text layouts. The reading and comprehension performance of 210 native Arab students assigned randomly to the different text layouts was compared. Results showed that the use of multicolumn setting (with medium or short line length) affected comprehension achievement but not reading and comprehension speed. Participants' comprehension scores were better for the single-column (with long line length) than for the multicolumn setting. However, no effect was found for interline spacing. The recommendations for appropriate print text format and layout in Arabic language based on the results of objective measures facilitating reading and comprehension performance is a single-column (with long line length) layout with no relevance of the interline spacing.

This study extended research on bilingual children’s narrative comprehension to text processing during retelling. A cross- and monolinguistic design allowed for the investigation of the association of various aspects of narrative comprehension with two types of pause occurring during oral retelling of a story heard in one language and retold in a second or in the same language. A sample of 95 bilingual (L1 German/L2 English) fourth-graders participated in the experiment. Comprehension was predominantly accomplished during listening, as children with L1 input outperformed children with L2 input, but they did not benefit from L1 in retelling. Children’s comprehension performance and corresponding pause patterns suggested that the duration of filled pauses dedicated to gist formation indicated efficiency of comprehension: The duration decreased with increasing comprehension. The findings allowed the conclusion that longer pauses during retelling did not buy time for comprehension.

The installation of muzzle brake changes the flow direction of propellant gas, which leads to a decline in the recoil force but an increase in the muzzle flow noise of the side rear. Therefore, the coordination between high efficiency and low harm of muzzle brake is one of the factors limiting its optimization. To address this problem, a numerical method for evaluating the comprehensive performance of muzzle brake targeting muzzle brake efficiency and impulse noise is proposed in the present study. The two performance indexes are calculated using a computational fluid dynamics (CFD)-computational aeroacoustics (CAA) coupled method. Afterwards, a corresponding experiment is conducted to verify its feasibility. Furthermore, the comprehensive performance of muzzle brakes with three different structures are analysed based on the two indexes obtained by the proposed numerical method. The results reveal that both indexes can be influenced by the structure of muzzle brakes. The increased braking efficiency is almost accompanied by increased impulse noise, but the functional relation is not linear dependence. Thus, the comprehensive performance can be improved by optimization of the structure. The evaluation method proposed in this paper has theoretical significance for optimizing muzzle brakes, which is of great engineering value.