Sharif Digital Repository

Solid-State Drives (SSDs) provide high performance, low power consumption, and hence are widely used in the I/O cache of enterprise storage systems and high performance servers. Although employing high performance SSDs in the I/O cache of storage systems significantly improves system performance, it comes with significant reliability threats for write operations upon power failures. In order to provide high level of reliability, storage architectures employ SSDs in I/O cache with RAID-1 configuration, however, such configuration only partially mitigates the reliability issues of the SSDs. In this thesis, we analyze the reliability of SSD-based I/O caches against power outage and high... 

One of the fundamental constraints that should have been in mind in flight scheduling is aircraft maintenance scheduling. Based on the accepted rules, regulations and flight safety, in a given period of time or after definite number of flight hours each aircraft should be sent to maintenance site. This influences the flight schedule. This research provides a comprehensive model for the flight scheduling. Given the flight schedule, number of the flights and aircrafts, maintenance center's capacity and other parameters such as each check's time, allowable flight days and allowable flight hours this model could determine each season's flight schedule and solve the aircraft routing problem.... 

Having an efficient and reliable system for oil-water separation is of crucial importance in oil and gas industry. Hydrocyclones have been used for more than a century to separate oil from water as well as sand from liquid or gas. The main objectives of this research are as follows: Determination the hydrocyclone principle of operation, based on computational fluid dynamic simulations. Hydrocyclones, in a spite of simple structure, are widely used in industry such as Petrochemical, Mining, Chemical Industries, Pharmacy, Food and Pulp Industries. The CALC BFC is one phase flow numerical code based on finite volume method and SIMPLEC algorithm. It was extended for simulating the two phase flow... 

Data storage systems are an essential part of any Information Technology (IT) infrastructure. Unavailability of these systems can directly lead to service disruption to customers and can be very costly in enterprise applications such as ebanking, online reservation systems, and mobile services. Modeling availability of disk subsystem is a major step in design of data storage systems. Previous modeling techniques have mainly focused on data unavailability or data loss due to double or multiple disk failures. In this thesis, we present both simulation and analytical modeling techniques to investigate the effect of serviceability on the overall availability of disk subsystems. The proposed... 

There are many parameters which are utilized to obtain a more reasonable performance for structures under earthquake excitations in seismic provisions. It is well recognized that the main character to design of structures under seismic excitation is probabilistic rather than deterministic; therefore, it should be determined if the probability of structural damages is decreased when such parameters change in design of structures. In this thesis, fragility curves are developed in order to evaluate these parameters. Fragility curves are employed for various probability parameters. These diagrams are utilized to demonstrate when a coefficient or a number of parameters are used to improve... 

In recent years, emerging Non-Volatile Memories (NVMs) have become promising alternatives for existing memory technologies. Due to shortcomings of SRAM memory in nanometer era,NVMs such as Phase-Change Memory (PCM) can be used in configuration memories of Field-Programmable Gate Arrays (FPGAs). Despite prominent features of emerging NVMs, they suffer from high write-power, high write-latency, and limited number of reliable write opera-tions. In addition, a dedicated Peripheral Circuit (PC) which is required to convert the NVM state to the equivalent voltage level can impose significant area and power overheads to FPGAs.In this thesis, a reliable power-efficient hybrid architecture employing... 

With increasing rate of digital information in the world, design, configuration, and networking of enterprise storage systems has become an essential part in designing data centers. The performance of data storage systems in serving incoming requests is one of the major parameters of such systems. A major metric to measure performance is response time. This parameter is, in particular, crucial in enterprise applications such as financial, credit, multimedia, and real-time applications. A common approach to enhance the performance of enterprise storage systems is improving the hit ratio of the system global memory using prefetching technique. Using prefetching technique, a data block is... 

Nowadays, enterprise storage systems are widely used in data centers such as databases, servers, and bank institutes. Due to mechanical activity of disk drives, these systems are one of the most power consumptive components in data centers. Prefetching and RAID, which are employed to enhance performance, are widely used in data storage systems. These two methods, however, impose significant energy overhead to the system due to the increased disk activity. In this thesis, we first elaborate shortcomings of prefetching and RAID methods. Then, we propose a new energy efficient and RAID-compatible prefetching method (LPTAP), which aims at improving performance and energy consumption. To evaluate... 

Performance and reliability are the major concerns in design of data storage systems. Using Redundant Array of Independent Disks (RAID) can enhance both performance and reliability. A commonly used configuration in RAID arrays is erasure codes to further enhance system reliability. Due to promising advantages of Solid-State Drives (SSDs)such as low power, shock resistance, and high I/O performance, designers have been encouraged to replace Hard Disk Drives (HDDs) by SSDs in RAID arrays. SSDs, however, suffer from limited endurance due to erase-before-write operation.In this thesis, we investigate the effect of stripe unite size and the number of disks of a RAID array on the endurance of SSDs... 

One of the most intrinsic challenges of flash-based Solid State Drives (SSDs) is erasebefore-write limitation and the limited endurance of flash chips. Wear leveling and garbage collection are two mechanisms implemented in SSD’s controller to enhance endurance and performance. While wear leveling attempts to distribute erasures across all blocks in an even manner, it imposes a new security challenge on SSD,which leads to the presence of invalid data blocks in flash chips. Therefore, some data blocks that are logically deleted by the user are still available in flash chips and can be recovered by software or hardware recovery tools.
In this paper, a new criteria named vulnerability time... 

Etiological studies proves the fact that Low Back Pain (LBP) is one of the most expensive and prevalent desease all over the world. This fact illustrates the reqiurment of the special effort in ordet to reducing the pain due to this problem. Finite element modeling of human spine is one the suitable methods to simulate the behavior of human spine in different loading conditions. These conditions could be different daily occupational tasks. There is two general viewpoint toward finite element modeling of human spine. The fisrt method focuses on the detailed geometry and mechanical properties of spine, while the other complexities such as detailed muscle forces are overlooked. The latter... 

Signifcant downscaling of CMOS technology to provide high performance along with low power consumption has been accompanied by reliability degradations such as increased noise sensitivity and reliability concern due to aging phenomena (transient and permanent failuers). In this regard, with huge number of configuration bits, Field-Programmable Gate Arrays (FPGAs) are more susceptible to aging since aging not only degrades the performance, but also it may additionally result in corrupting the configuration cells and thus causing permanent circuit malfunctioning. While several works have investigated the aging effects in Look-Up Tables (LUTs), the routing fabric of these devices is seldom... 

Significant increase of static power with downscaling of transistor feature size and threshold voltage has lead to the end of Dennard scaling. This obstacle has put a Power Wall to further integration of CMOS technology in Field Programmable Gate Arrays (FPGAs). An efficient solution to cope with this obstacle is to apply power gating to the inactive fractions of a single die, referred to as Dark Silicon. Previous studies employing power gating on SRAM-based FPGAs have primarily focused on using large-input Look-up Tables (LUTs) which suffer from poor logic utilization, and subsequently, limiting the benefits of power gating techniques. This thesis proposes a heterogeneous Power-Efficient... 

Nowadays, embedded processors are widely used in wide range of domains from low-power to safety-critical applications. By providing prominent features such as variant peripheral support and flexibility to partial or major design modifications, Field-Programmable Gate Arrays (FPGAs) are used in industry for implementing either an entire embedded system or a Hardware Description Language (HDL)-based processor, known as soft-core processor. FPGA-based designs, however, suffer from high power consumption, large die area, and low performance that hinders common use of soft-core processors. In this thesis, we present an efficient reconfigurable architecture to implement embedded processors in... 

Traffic safety is one of the fundamental part of the transportation planning which is led to lowest the number of crashes and its following consequences by in-depth studying. Thus, determining the severity of accidents, including damage, injury and fatal injury is very important. The aim of this study is analysis of the accident-injury severities in single-vehicle and multi-vehicle crashes and providing the policies in Iran. The approach used in this study to select the most effective parameters of the injury-severity is based on the data gathered in Iran Road Maintenance and Transportation Organization during the year 2011. Accident probabilistic model based on analysis of relations among... 

Time based competition is considered as an importance strategy in the contemporary manufacturing systems. Reconfigurable Manufacturing System (RMS) is a new paradigm that not only produces the products with high productivity but also allows for rapid response to market changes. Despite the large impact on company performance, the importance of due date setting and order planning processes and related decisions is underexposed in the literature of RMS. The most important contribution of this thesis is orders planning under setting due date in make-to-order RMS environment. This thesis seeks to determine the best selection of several orders, their sequencing and corresponding configurations... 

Emerging Solid State Drives (SSDs) have performance advantages over traditional Hard Disk Drives (HDDs). Higher price per capacity and limited lifetime, however, prevents enterprise data centers to entirely replace HDD-based storage subsystems with SSDs. Thus,SSD-based caching has been widely employed in data centers to benefit from higher performance of SSDs while minimizing overall cost. Input/Output (I/O) workloads exhibit unpredictable and highly random behavior which makes conventional algorithms such as Least Recently Used (LRU) not able to provide high hit ratio as they employ linear localities.In addition to poor performance, such algorithms also shorten SSD lifetime with unnecessary...