limit number of workers, not just number of cpus

[jesse]

We have a farm of 20 worker nodes and 160 cpus.  We have a plugin that can only run on 5 worker nodes at one time.  Is it possible to limit the number of workers that the job will get sent to at one time?  I've seen the cpus restriction, but it does not see that this will work well enough. 

I know I have the following options, but I was hoping for a better solution:

• Limit the number of cpus to 5, thus insuring that only 5 workers would ever work on the job.  Sadly this would lose 35 potential procs.
• Explicit run on 5 specific workers.  This would be painful if the wrong workers were chosen at submission time wherein 5 nodes might be free, but the wrong 5.

Any Help would be appreciated.
Cheers,
jesse

[jesse]

I've now read more of the Administration pdf.  I see that clusters might be useful in this case.  Is it possible to limit a job to a cluster?

[eric]

Restrictions are how you can limit a job to run on a particular cluster. Just put the cluster name in the "restrictions" field when you submit the job.

[jesse]

Aha!
Since I am new to clusters I did not realize they could be used in the restrictions list as well. 
Thank you!