A common trend in the design of large-scale clusters is to use a
high-performanc e data network to integrate the processing nodes in a
single parallel computer.  In these systems the performance of the
interconnect can be a limiting factor for the input/output (I/O),
which is traditionally bottlenecked by the disk bandwidth.  In this
paper we present an experimental analysis on a 64-node AlphaServer
cluster based on the Quadrics network (QsNET) of the behavior of the
interconne ct under I/O traffic, and the influence of the placement of
the I/O servers on the overall performance.  The effects of using
dedicated I/O nodes or overlapping I/O and computation on the I/O
nodes are also analyzed.  In addition, we evaluate how background I/O
traffic interferes with other parallel applications running
concurrently.  Our experimental results show that a correct placement
of the I/O servers can provide up to 20% increase in the available I/O
bandwidth.  Moreover, some important guidelines for applications and
I/O servers mapping on large-scale clusters are given.