Research

Elizabeth Varki
Department of Computer Science
University of New Hampshire
Kingsbury Hall
Durham, NH 03824

Phone: (603) 862-2319
Email: varki@cs.unh.edu
www: www.cs.unh.edu/~varki

My area of expertise is performance evaluation. I evaluate the performance of computer and communication systems, storage devices, and software systems. I am a modeler: real-world is complex and it is difficult to understand what features of the real-world drives performance. For example, when you click a link on your web browser, what determines the speed with which the page is downloaded on your computer - the speed of your computer, or the network bandwidth, or the speed of the web server, or some other factor? This leads to further questions: what determines the speed of your computer - the CPU speed or the cache size or the memory bus speed - leading to futher evaluation at lower levels. There are many, many parameters in a real system, which makes it difficult to see the forest for the trees. I determine what parameters are essential to determining the performance of the real-world system under consideration. I then develop a mathematical model that incoporates only those parameters that drive the performance. Thus, my model is an abstraction of the real system that incoporporates the essential parameters that drive performance. Once a model is validated, it can then be used to understance the behavior of the real system.

I develop performance models which compute mean performance measures such as response time and throughput. These are articulated by queueing models. When computing performance of distributed systems - computers around the globe connected by the Internet - I use graph models. Once I develop the model, I use existing algorithms, to compute performance measures from the model. If algorithms/tools to compute mean performance measures from the model do not exist, then I develop (or try to develop) the algorithm.

I develop new technology if existing technology is not keeping pace with improvements in hardware and software. For example, my student and I have developed RAIDX for arrays of dissimilar disks since RAID was developed for arrays of similar disks.

Listed below are my papers, classified by topic:

Computing Ethics

RAIDX: RAID for heterogenous array of disks

We propose a new organization for organizing an array of disks of different types, sizes, and speeds. RAIDX does not stripe data across disks, it bundles chunks of data across disks.

GPSonflow: Geographic Positioning of Storage for optimal nice flow

We develop an app to move petabyte-scale data from sender to receiver via the internet cheaply.

Prefetch cache replacement technique

Prefetch cache

Arrival queues

Fibre channel

RAID

Fork-Join queues

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