39 research outputs found
Striping Doesn't Scale: How to Achieve Scalability for Continuous Media Servers with Replication
Multimedia applications place high demands for QoS, performance, and
reliability on storage servers and communication networks.
These, often stringent, requirements make design of cost-effective and
scalable continuous media (CM) servers difficult. In particular, the
choice of data placement techniques can have a significant effect on the
scalability of the CM server and its ability to utilize resources
efficiently.
In the recent past, a great deal of work has focused on ``wide'' data
striping as a technique which ``implicitly'' solves load balancing
problems; although, it does suffer from multiple shortcomings.
Another approach to dealing with load imbalance problems is replication.
The main focus of this paper is a study of scalability characteristics of
CM servers as a function of tradeoffs between striping and replication.
More specifically, striping is a good approach to load balancing while
replication is a good approach to ``isolating'' nodes from being dependent
on other system resources.
The appropriate compromise between the degree of striping and the degree
of replication is key to the design of a scalable CM server. This is the
topic of our work.
Also cross-referenced as UMIACS-TR-99-4
A Performance Study of Dynamic Replication Techniques in Continuous Media Servers
Multimedia applications are emerging in education, information
dissemination, entertainment, as well as many other applications. The
stringent requirements of such applications make design of cost-effective
and scalable systems difficult, and therefore efficient adaptive and
dynamic resource management techniques can be of great help in improving
resource utilization and consequently improving performance and
scalability of such systems. In this paper, we focus on threshold-based
policies, for dynamic resource management, and specifically, in the
context of continuous media (CM) servers. Furthermore, we propose a
mathematical model of user behavior and show, through a performance study,
that not only does the use of this model in conjunction with dynamic
resource management policies improves the system's performance but that
it also facilitates significantly reduced sensitivity to changes in:
(a) system architecture, (b) workload characteristics,
(c) skewness of data access patterns,
(d) frequency of changes in data access patterns, and (e) choice of
threshold values. We believe that not only is this a desirable property
for a CM server, in general, but that furthermore, it suggests the
usefulness of these techniques across a wide range of continuous media
applications.
Also cross-referenced as UMIACS-TR-98-6
Design of Scalable Continuous Media Servers with Dynamic Replication
Multimedia applications place high demands for quality-of-service (QoS),
performance, and reliability on systems. These stringent requirements
make design of cost-effective and scalable systems difficult.
Therefore efficient adaptive and dynamic resource management techniques
in conjunction with data placement techniques can be of great help in
improving performance, scalability and reliability of such systems.
In this paper, we first focus on data placement.
In the recent past, a great deal of work has focused on "wide" data
striping as a way of dealing with load imbalance problems caused by
skews in data access patterns. Another approach to dealing with load imbalance
problems is replication. The appropriate compromise between the degree
of striping and the degree of replication is key to the design of
scalable continuous media (CM) servers. In this work we focus on evaluation
of this compromise in the context of a hybrid CM server design.
Changes in data access patterns lead to other questions:
(1) when should the system alter the number of copies of a CM object, and
(2) how to accomplish this change. We address (1) through an adaptive
threshold-based approach, and we use dynamic replication policies in
conjunction with a mathematical model of user behavior to address (2).
We do this without any knowledge of data access patterns and with
provisions for full use of VCR functionality. Through a performance
study, we show that not only does the use of this mathematical model
in conjunction with dynamic resource management policies improves the
system's performance but that it also facilitates reduced sensitivity
to changes in:(a) workload characteristics, (b) skewness of data access
patterns, and (c) frequency of changes in data access patterns.
We believe that not only is this a desirable property for a CM server,
in general, but that furthermore, it suggests the usefulness of these
techniques across a wide range of continuous media applications.
(Cross-referenced as UMIACS-TR-2001-21
Multi-path Streaming: Is It Worth the Trouble?
s to the receiver. We note that such paths do not have to be completely disjoint, i.e., it is sufficient for them to have disjoint points of congestion or bottlenecks. Existence of multiple paths with disjoint bottlenecks includes the following potential benefits: (a) reduction in correlation between consecutive packet losses which we believe will lead to improvements in the quality of delivered data, (b) increased throughput, and (c) ability to adjust to variations in congestion patterns on different parts of the network. In this work, our focus is on providing the fundamental understanding and on characterizing the benefits of the multi-path approach to streaming of pre-stored continuous media data over wide-area networks (under the setup described below) . More specifically, we focus on loss characteristics as they are an indication of the resulting quality of the delivered data stream. We believe that the understanding of loss characteristics under a multi-path approach is non-tr