"The purpose of this article is to introduce Single
System Image (SSI) Clustering. First we will look at what
clustering is and the various problems a clustered platform solves.
Then we generally define what a SSI cluster is and look at various
forms and degrees of SSI. From there we focus on the Open SSI
Cluster Project - the goals, the benefits SSI clustering can bring
and the application areas for SSI clustering. We complete the paper
with an architectural overview of the SSI cluster project.
The term clustering, with no adjective specifying the type of
clustering, means different things to different groups. Below is a
short discussion of high performance (HP) clusters, load-leveling
clusters, web-service clusters, storage clusters, database clusters
and high-availability (HA) clusters. All of these have a few things
in common that distinguish clusters from other computing
platforms.
Clusters are typically constructed from standard computers, or
nodes without any shared physical memory. That, combined with the
characteristic of running an OS kernel on each node, distinguishes
a cluster from a NUMA (Non-Uniform Memory Architecture) or SMP
(Symmetric Multi-Processor) platform (of course a cluster could be
constructed from NUMA or SMP nodes). The "purpose" of a cluster is
for the individual nodes to work together to better provide HA
(High Availability), HP (High Performance), parallel processing or
parallel web servicing. Finally, a cluster is different from a
client-server distributed computing environment in that each of the
cluster platform solutions is more peer-to-peer, typically with a
sense that each node is a member of a larger system."
