Some Relief For Cluster Consternation

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From the things to consider while on vacation department

Last fall when my daughter started school, she came home and said the teacher recommended students get a graphing calculator. Mind you, it was not the hundred bucks for the calculator that promoted me to grab a pencil and paper and say "Back in my day, this was our graphing calculator. No batteries needed, you can even keep the stylus on your ear, and as a bonus feature it has an undo tip as well", but rather the idea that the pencil and paperwas becoming a lost art. I mean if you are on desert island and need to plot a parabola, where are you going to find a graping calculator? (You might be wondering what this has to do with clusters? read on.)

At that point, my wife joined the conversation and mentioned that the teachers probably used graphing calculator in high school and college as well. Sigh. Nothing like feeling old. It seems when I was in my college years, there were classes devoted to learning how to plot equations on these large toggle switch laden things called minicomputers. We have improved a bit since then and graphing calculators are one example. In my daughters school, graphing calculators are used to teach subjects, they are not a subject per-se. If I put my analogy hat on for a moment, I think back to the day, with all their consternations, minicomputers let me do better math and science. Graphing calculators can now handle many of those chores and presumably will help my daughter do better math and science. Thinking about clusters, with all their modern day consternations, I have to ask what is stopping clusters from being a useful tool. Instead of plotting equations, however, we can calculate and plot entire solution spaces right in the classroom.

Sidebar One: Big Word Alert
Consternation - a sudden, alarming amazement or dread that results in utter confusion; dismay. That is pretty much how I sum up those that know nothing about clusters. Indeed, racks of blinking lights, wires and fans are still and alarming amazement to me.

Education is Obvious

One obvious one solution is enhanced education. Ahh, well, there is the catch. Check your favorite search engine for "Beowulf Cluster Courses" or "Linux Cluster Courses" and some of the top responses are people asking where to find such a course. There were some hits, however, I'll mention those later.

So why no cluster courses? I propose three reasons. First, up until about 3 years ago, clusters were a fast moving target. They are still moving, but they not quite as fast. There are now some "reproducible" methods that include prebuilt distributions and tool-kits. Beyond node provisioning, things are a bit more settled, but compilation and invocation issues can still vary widely. For instance, multiple MPI versions often can cause confusion among users, unless some type of environment management is used (e.g See the Modulespackage) users usually have to contend with making sure they know where the various MPI libraries/binaries live on the cluster. (Nothing like trying to start an LAM/MPI job with and MPICH version of mpirun.) {mosgoogle right}

A second issue is finding people to teach about clusters. Most of the rugged individualists and cluster pioneers, are too busy to teach or write about clusters. There are exceptions of course, but in general, with clusters it seems you are either plowing the fields or building the plow. Taking time to explain your craft just does not seem to fit in the workday.

The final issue is the scope of what can be taught. To date, most classes or tutorials that I have seen have been aimed at setting up and administering a basic cluster. Interestingly, there is no "How to Build a Cluster" Tutorial at SC2006 this past year (there have been in years past). When one talks about clusters, there are really two sub-groups that need to be addressed; administrators and users. The administrators are interested in provisioning the cluster to meet the users needs and minimizing the work needed to maintain and upgrade the cluster. The users on the other hand want to run codes and use the cluster effectively. There is some overlap, but in general, these are two very different agendas. Obviously, the majority of cluster courses have been on provisioning a cluster which needs to happen before you can address the "domain expert" (i.e. users) issues. Fortunately, I believe the impact of these issues are lessening. Cluster recipes have settled down a bit and more people know how to "do clusters." The Beowulf mailing list and of course Cluster Monkeyare good resources as well. In my opinion, the real challenge is going to be packaging and bringing this information to the domain experts. Economic issues aside, clusters should be as easy as using printing calculators

Apprenticeships Do Not Scale Well

As I mentioned above, finding people to teach about clusters is difficult. This situation then begs the question, In the absence of courses, how does one learn about clusters?There seem to be two ways, both of which do not sale very well. First, you have the old fashion apprenticeship. Working with someone who has clusters (and knows what they are doing) is great way to learn. The other is to set off by yourself and with the help of a mailing list of two build your own cluster. Both approaches take time. The do it yourself approach will allow you to make mistakes which of course is how you learn about most things.

It should be noted however, that most cluster people be they users or administrators usually don't go into such projects blindly. They bring with them some "carry over" from other areas of computing. Indeed, a large portion of "cluster know-how" comes from other established areas of computing. They all have some level of an educational infrastructure (manuals, mailing lists, freely available software, and even courses) that can be leveraged by those wanting to learn about clusters. Consider the following topic list.

  • Message Passing Interface (MPI)- Because MPI has been around before clusters hit the big time, there are numerous books and classes that facilitate learning MPI. Also, PVM (Parallel Virtual Machine) was a great way to connect workstations and learn about parallel computing.
  • Compilers- Most cluster experts have a good understanding of compilers and building code. Understanding that the long stream of error messages can be due to missing library (and easily fixed) prevents the sense of overwhelm that comes with trying to build that new software package in your environment.
  • Operating System Administration- Opportunities to learn about operating systems are plentiful. Three inch thick books are in good supply as well as certification classes and training
  • Commodity Hardware- Most clusters use off-the-shelf hardware. Resources for understanding commodity hardware are also plentiful. Although nothing works like have a motherboard or two with which to test ideas.
  • Schedulers- Resource scheduling has been around ever since people started sharing computers. There are resources to help learn about schedulers and like most things, a little hands-on time does wonders.
  • Networking - Networking is perhaps the toughest area to find good information -- even in cluster courses. For many other cases non-optimal network performance works quite well for just browsing the web or transferring a file. Although much of Linux networking is plug-and-play, there is room for optimization when it comes to clusters. High end interconnect networks have in the past been even more obscure. Fortunately the market seems to be focusing on either 10 GigE or Infiniband solutions and many of the high end network companies are moving in this direction as well.

In my opinion a good cluster course puts all this together and provides insights on how to weave the essential parts of these components into well oiled cluster machine. Of course, there are some exclusive cluster issues which deal with parallel computing, but a good grasp of the above issues is creates a solid foundation.

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