[Beowulf] Computation on the head node
Jeffrey B. Layton
laytonjb at charter.net
Mon May 19 07:40:47 EDT 2008
Joe Landman wrote:
> Perry E. Metzger wrote:
>> checking. A very fast RAID array may be in order -- or it may be
>> completely unnecessary. One can't know without understanding one's
>> application intimately, and that requires testing.
> Of course. But there are quite a few people/groups on this list with
> decades of HPC experience that might have an inkling if a USB or
> similar connected drive "is a good idea" for an app, even prior to
> running it. Benchmarking is important, but it is important that the
> benchmark represent real runs. Experience can provide a rough guide
> in the case of no benchmark data availability. With clusters, you run
> into the very real problem of IO resource contention, quite quickly.
> Putting lower end IO devices in there rarely makes sense. Sure, you
> can benchmark it, and you should if possible. But it is also not a
> bad idea to listen to people whom have been working on this stuff for
> a while, they might have a clue about these things.
Here comes the $64 question - how do you benchmark the IO portion of your
code so you can understand whether you need a parallel file system, what
of connection do you need from a client to the storage, etc. This is a
problem and one in which I have an interest.
The best way I've found is to look a the IO pattern of your code(s). The
I've found to do this is to run an strace against the code. I've written
analyzer that gives you a higher-level view of what's going on with the IO.
I'm also working on a tool that can take the strace output and create a
that will run in a similar manner to the original code but actually
IO of the original code using dummy data. This allows you to "give" away
a simple dummy code to various HPC storage vendors and test your
This code is taking a little longer than I'd hoped to develop :(
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