Hardware Reference
In-Depth Information
FIGURE 4.3: The choice of I/O interface by job size breakdown as captured
by Darshan on Intrepid.
choices by job size based on data captured by Darshan during the period of
January through March 2010. As job size tends to increase in number of MPI
ranks though, users start to adopt MPI-IO. MPI-IO and other I/O libraries,
which use it significantly, help scale up the eciency of I/O on Intrepid and
Mira by \automating" some of the key performance rules for GPFS which is
to organize data into file system block-sized aligned chunks so that there is
minimal lock contention and 4-MiB request sizes.
4.5 Workloads/Applications
Given that ALCF is an open science computing facility, users are drawn
from many areas of science. The wide variety of applications results in a varied
I/O workload for the systems. The users and applications may be internal
or external to ANL, so it is dicult to obtain detailed information about
the I/O any particular application does. Consider Figure 4.4, which clearly
shows that the ALCF workload varies over the course of the year. This relates
to various projects running heavily in a campaign mode and then once the
campaign is finished or much of their CPU allocation is exhausted, other
projects become the primary consumers of resources and the overall system
I/O workload changes. Intrepid's I/O prole shows two major concepts; (1)
