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Interview with JAWS early users Duane Stevens and Guang-Xia (Jax) Cao (18 July 2007)

Earlier this year, the powerful JAWS was opened up to our users. JAWS is the 11th fastest supercomputer in the world, according to the Top500 list, published in November 2006. Read an interview with some of the first users from the UH campus to get an account and start running their jobs on JAWS, to learn their experiences with this powerful machine:

UH-HPC: Please tell us who you are; and a little about your research, what you were doing on JAWS, so our readers will have a context.

Duane: I am Duane Stevens, Professor of Meteorology, and distinctly recall the 2004 Halloween eve during the flood. A thunderstorm dropped a lot of rain onto the island, particularly in upper Manoa Valley. Another meteorology student took movies of the flooding at his home. Both we and the National Weather Service are interested in the effect of both heavy rainfall and hurricanes on Hawaii.

Jax: My name is Guangxia Cao. I am in the Geography Department and major in Climatology. I work closely with Dr. Stevens in this cross disciplinary project, simulating the rainfall and the effects it had on the island. We want to correctly forecast the thunderstorm. To date, there is no successful protocol to predict the local weather conditions. In this study, we use the Weather Research Forecast (WRF) model, to simulate the event. The long-range goal is to predict them.

Duane: By the way, WRF is an open source model you can get download it from www.wrf-model.org.

UH-HPC: So, had you used MHPCC resources before?

Jax: Yes, in my recently completed PhD studies. It was impossible to accomplish my work without it.

UH-HPC: Which systems had you used previously?

Jax: Tempest, with the help of Dr. Stevens and the Engagement Grant from HPC.

UH-HPC: What kind of supercomputer is Tempest?

Jax: Tempest is an IBM cluster. The IBM cluster has large memory per node, which is needed for running sophisticated weather models.

UH-HPC: Then you transferred your model to JAWS? What kind of supercomputer is that?

Jax: JAWS is a Dell cluster. It is a newly established platform. Everything became stable only by May 2007. For example, users had to specify the file extension themselves until May for the FORTRAN compiler.

UH-HPC: What did you have to do to transfer your account to JAWS?

Jax: That was very easy. I just wrote a letter to the user accounts, and all was transferred.

UH-HPC: Does an account on JAWS require a NAC?

Jax: Yes.

UH-HPC: You had already completed a NAC to use Tempest; did you have to re-submit it to get a JAWS account?

Jax: No. The one I had submitted for Tempest was still valid for my JAWS account.

UH-HPC: You had to transfer all your data and software over to the JAWS system. How did that go?

Jax: I had to do it myself. It was very challenging. It took about a month to fully compile the WRF model. Mainly that was because the compiler was different. JAWS uses ifort, an Intel Fortran compiler, which is not as popular as, say the IBM xlf compiler used on Tempest Also, there were differences because the number of processors per node was different, making some of my Tempest experience not directly transferable to JAWS. Tempest had 16 processers per node (P3) or 32 processors per node (P4), while JAWS has 4 processors per node.

UH-HPC: Did you work on your own, or did the staff at MHPCC help you?

Jax: The staff at MHPCC helped, mostly through email. In one case, when I transferred my account to JAWS, my login node had a problem. My parallel job wouldn't submit. I emailed the problem to the MHPCC help desk, and it was fixed easily. That happened with a few other problems too.

UH-HPC: Was there online help available?

Jax: The general introduction to JAWS was helpful, and the account information was helpful.

Duane: There isn't much documentation available on FORTRAN compilers.

UH-HPC: Now that it's going,what differences do you see between running on Tempest and running on JAWS?

Jax: JAWS is absolutely faster! It is 2-3 times faster. I was surprised. At first, when I saw only 4 processors per node, I didn't expect a huge speed-up, but even a single processor in JAWS is faster than any other machine's single processor. The people at MHPCC are doing a good job.

Duane: Months ago, you could get on JAWS easily and run many jobs.

Jax: It's getting harder now. I have "normal" account status (vice priority status). Now it takes a whole day for my jobs to process because of the increased traffic.

UH-HPC: What advice would you give the new JAWS user?

Jax: If you are using a FORTRAN program, learn about the Intel compiler ifort to prepare. Otherwise, your program should be easily transferable.