General Comments, Caveats, & Recommendations
- Since about mid-April 2007, we have started doing daily
backups of all active user directories in the /home area only. The rest (e.g.,
/scratch/username/*) is your responsibility to move to our tape archive or
elsewhere, if need be.
- Know your program. Know, approximately that is, how much
memory, how much I/O and disk space, how much CPU and wall-clock time it needs
for a run. If it runs in parallel mode, it is important to know how well your
program's performance scales as you increase the number of processors. At the
very least try to find out. We will help. Also, be aware that in submitting
parallel MPI batch jobs there are several ways to indicate how you want your
job distributed across the available nodes. Read more on this important topic
in the subsection on batch jobs, "Task Distribution across Nodes".
- Prefer 64-bit executables. Always prefer to construct
64-bit executables, if you have a choice. These, and not the 32-bit versions,
include all the high performance features of the Power5+ architecture, as well
as allow for a very large memory address limit. With 32-bit executables you're
stuck at 4 gigabytes. But this limit is frequently exceeded when solving large
problems. It is for these reasons that we consistently use the -q64 compiling
option below. By the way, this 64-bit issue has nothing to do with numeric data
- Prefer using only Bourne shell compatibles. For your
scripts, please use only Bourne Shell compatibles or derivatives: ksh (Korn),
sh (Bourne). The Korn shell is the standard Unix shell on hydra. Also, even
though generic bash is in many ways desirable, on AIX it has some pesky
- We strongly discourage you from transfering startup scripts
(.login, .profile, etc.) from other systems, or casually changing the ones that
your account comes with, unless you understand the effects of those changes.
And don't expect PBS or LSF batch scripts to work on this cluster. This
admonition also applies to configuration files related to various applications,
such as the ones used by ABAQUS, CFX, etc. If you need help let us know.