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Center for High Throughput Computing

Additional HPC Guides

HPC Cluster Overview


  1. High-Performance Computing at CHTC
  2. New HPC Configuration
  3. HPC User Policies
  4. HPC Hardware and Configuration
  5. Data Storage and Management

High-Performance Computing at CHTC

The CHTC high-performance computing (HPC) cluster provides dedicated support for large, singular computations that use specialized software (i.e. MPI) to achieve internal parallelization of work across multiple servers of dozens to hundreds of cores.

Is high-performance computing right for me? Only computational work that fits that above description is permitted on the HPC. All other computational work, including single and multi-core (but single node) processes, that each complete in less than 72 hours on a single node will be best supported by our larger high-throughput computing (HTC) system (which also includes specialized hardware for extreme memory, GPUs, and other cases). For more information about high-throughput computing, please see Our Approach.

To get access to the HPC, please complete our Large-Scale Computing Request Form. After your account request is received, our Research Computing Facilitators will follow up with you and schedule a meeting to discuss the computational needs of your research and connect you with computing resources (including non-CHTC services) that best fit your needs.

HPC User Policies

Below is a list of policies that apply to all HPC users.

1. Do Not Run Programs On The Login Nodes
When you connect to the HPC, you are connected to a login node. The HPC login nodes have limited computing resources that are occupied with running Slurm and managing job submission.

Users should only run basic commands (like tar, cp, mkdir) on the login nodes. The execution of scripts, including cron, software, and software compilation on the login nodes is prohibited (and could VERY likely crash the head node). However, users may run small scripts and commands (to compress data, create directories, etc.) that run within a few minutes but their use should be minimized when possible. If you are unsure if your scripts are suitable for running on the login nodes, please contact us at chtc@cs.wisc.edu.

CHTC staff reserve the right to kill any long-running or problematic processes on the head nodes and/or disable user accounts that violate this policy

Violation of these policies may result in suspension of your account.

2. The HPC Is Reserved For MPI-enabled, Multi-node Jobs
HPC users should not submit single-core or single-node jobs to the HPC. Users will be asked to transition this kind of work to our high-throughput computing system.

3. HPC File System Is Not Backed-up
All files on the HPC should be treated as temporary and only files necessary for actively running jobs should be kept on the file system. Once your jobs complete, your files should be removed from the HPC. Campus researchers have several options for data storage solutions, including ResearchDrive which provides up to 5TB of storage for free. Our guide Transferring Files Between CHTC and ResearchDrive provides step-by-step instructions for transferring your data to and from the HPC and RsearchDrive.

CHTC Staff reserve the right to remove any significant amounts of data on the HPC Cluster in our efforts to maintain filesystem performance for all users, though we will always first ask users to remove excess data and minimize file counts before taking additional action.

4. Fair-share Policy
To promote fair access to HPC computing resources, all users are limited to 10 concurrently running jobs at a time. Additionally, user are restricted to a total of 600 cores across all running jobs. Core limits do not apply on research group partitions of more than 600 cores.

5. Job Priority Policy

A. User priority decreases as the user accumulates hours of CPU time over the last 21 days, across all queues. This “fair-share” policy means that users who have run many/larger jobs in the near-past will have a lower priority, and users with little recent activity will see their waiting jobs start sooner. We do NOT have a strict “first-in-first-out” queue policy.

B. Job priority increases with job wait time. After the history-based user priority calculation in (A), the next most important factor for each job’s priority is the amount of time that each job has already waited in the queue. For all the jobs of a single user, these jobs will most closely follow a “first-in-first-out” policy.

C. Job priority increases with job size, in cores. This least important factor slightly favors larger jobs, as a means of somewhat countering the inherently longer wait time necessary for allocating more cores to a single job.

HPC Hardware and Configuration

The HPC Cluster consists of two login nodes and many compute (aka execute) nodes. All users log in at a login node, and all user files on the shared file sytem are accessible on all nodes. Additionally, all nodes are tightly networked (56 Gbit/s Infiniband) so they can work together as a single "supercomputer", depending on the number of CPUs you specify.

Login Nodes

The two login nodes for the cluster are:

  • hpclogin1.chtc.wisc.edu
  • hpclogin2.chtc.wisc.edu

For more details on logging in, see the “Connecting to CHTC” guide linked above.

Execute Nodes

Only execute nodes will be used for performing your computational work. The execute nodes are organized into several "partitions", including the univ2, pre, and int partitions which are available to all HPC users as well as research group specific partitions that consist of researcher owned hardware and which all HPC users can access on a backfill capacity via the pre partition (more details below).


Partition p-name # nodes (N) t-max t-default max nodes/job cores/node (n) RAM/node (GB)
University 2 univ2 148 7 days 1 day 16 20 128
Interactive int 6 1 hr 1 hr 1 20 128
Pre-emptable (backfill) pre 316 24 hrs 4 hrs 16 20 128
Owners unique 124 7 days 24 hrs unique 20 128
Astronomy Dept (differs) astro3 24 4 days 24 hrs 16 20 128
  • univ2 consists of our second generation compute nodes, each with 20 CPU cores of 2.5 GHz and 128 GB of RAM. Like univ, jobs submitted to this partition will not be pre-empted and can run for up to 7 days.

  • int consists of two compute nodes is intended for short and immediate interactive testing on a single node (up to 16 CPUs, 64 GB RAM). Jobs submitted to this partition can run for up to 1 hour.

  • pre (i.e. pre-emptable) is an under-layed partition encompassing all HPC compute nodes. This partiton is intended for more immediate turn-around of shorter and somewhat smaller jobs, or for interactive sessions requiring more than the 30-minute limit of the int partition. Jobs submitted to pre are pre-emptable and can run for up to 24 hours. pre partition jobs will run on any idle nodes, including researcher owned compute nodes nodes, as back-fill meaning these jobs may be pre-empted by higher priority jobs. However, pre-empted jobs will be re-queued when submitted with an sbatch script.

Operating System and Software

All nodes in the HPC Cluster are running CentOS 7 Linux.

The SLURM scheduler version is 20.02.2.

To see more details of other software on the cluster, see the HPC Software page.

Data Storage and Management

Data space in the HPC file system is not backed-up and should be treated as temporary by users. Only files necessary for actively-running jobs should be kept on the file system, and files should be removed from the cluster when jobs complete. A copy of any essential files should be kept in an alternate, non-CHTC storage location.

Each user will receive two primary data storage locations:

  1. /home/username with an initial disk quota of 100GB and 10,000 items. With the exception of software, all of the files needed for your work, such as input, output, configuration files, etc. should be located in your /home directory.

  2. /software/username with an initial disk quota of 10GB and 100,000 items. All software, library, etc. installtions should be written to and located in your /software directory.

To check how many files and directories you have in your /home or /software directory see the instructions below.

Increased quotas to either of these locations are available upon email request to chtc@cs.wisc.edu. In your request, please include both size (in GB) and file/directory counts. If you don't know how many files your installation creates, because it's more than the current items quota, simply indicate that in your request.

CHTC Staff reserve the right to remove any significant amounts of data on the HPC Cluster in our efforts to maintain filesystem performance for all users, though we will always first ask users to remove excess data and minimize file counts before taking additional action.

Local scratch space of 500 GB is available on each execute node in /scratch/local/$USER and is automatically cleaned out upon completion of scheduled job sessions (interactive or non-interactive). Local scratch is available on the login nodes, hpclogin1 and hpclogin2, also at /scratch/local/$USER and should be cleaned out by the user upon completion of compiling activities. CHTC staff will otherwise clean this location of the oldest files when it reaches 80% capacity.

Tools for managing home and software space

You can use the command get_quotas to see what disk and items quotas are currently set for a given directory path. This command will also let you see how much disk is in use and how many items are present in a directory:

[username@hpclogin1 ~]$ get_quotas /home/username /software/username

Alternatively, the ncdu command can also be used to see how many files and directories are contained in a given path:

[username@hpclogin1 ~]$ ncdu /home/username
[username@hpclogin1 ~]$ ncdu /software/username

When ncdu has finished running, the output will give you a total file count and allow you to navigate between subdirectories for even more details. Type q when you're ready to exit the output viewer. More info here: https://lintut.com/ncdu-check-disk-usage/