Two user-visible changes are planned for the Casper cluster in the coming month. The first change will be the removal of the deprecated casper.ucar.edu domain name for SSH login usage. The current recommended domain name for accessing Casper is casper.hpc.ucar.edu. The old address will be retired as early as May 21, so now is the time to switch to the casper.hpc.ucar.edu domain when using ssh/scp/rsync and similar commands if you have not done so already.

The second change will come on May 27, when we will disable swap space for high-throughput computing PBS jobs on Casper. For users who are unaware, currently if your program exceeds your requested memory in your HTC PBS job, any additional allocated data storage will “spill” into swap space on disk. This mechanism prevents your job from failing but also results in dramatically slower processing, which has been a source of confusion for some users. Thus, we plan to disable swap to simplify the user experience and yield more consistent job outcomes. File-based spill to disk, as can be done by libraries like Dask, will still be possible after the change, and there are currently no plans to disable swap on GPU nodes.