Photo: Image of the Glenn supercomputer

The Ohio Supercomputer Center's IBM Cluster 1350, named "Glenn", features AMD Opteron multi-core technologies. The system offers a peak performance of more than 54 trillion floating point operations per second and a variety of memory and processor configurations. The current Glenn Phase II components were installed and deployed in 2009, while the earlier phase of Glenn – now decommissioned – had been installed and deployed in 2007.

<--break->2014/07/12: 222 nodes of Glenn have been removed. 
In preparation for the delivery and installation of 240 nodes for Ruby, we have removed 222 nodes of Glenn. This reduction in available compute is required in order to ensure we stay under power limits at the SOCC and are able to physically configure the space in advance of the delivery of new hardware.


The current hardware configuration consists of the following:

  • 436 System x3455 compute nodes
    • Dual socket, quad core 2.5 GHz Opterons
    • 24 GB RAM
    • 393 GB local disk space in /tmp
  • 2 System x3755 login nodes
    • Quad socket quad core 2.4 GHz Opterons
    • 64 GB RAM
  • Voltaire 20 Gbps PCI Express adapters

There are 36 GPU-capable nodes on Glenn, connected to 18 Quadro Plex S4's for a total of 72 CUDA-enabled graphics devices. Each node has access to two Quadro FX 5800-level graphics cards.

  • Each Quadro Plex S4 has these specs:
    • Each Quadro Plex S4 contains 4 Quadro FX 5800 GPUs
    • 240 cores per GPU
    • 4GB Memory per card
  • The 36 compute nodes in Glenn contain:
    • Dual socket, quad core 2.5 GHz Opterons
    • 24 GB RAM
    • 393 GB local disk space in '/tmp'
    • 20Gb/s Infiniband ConnectX host channel adapater (HCA)

How to Connect

To connect to Glenn, ssh to

Batch Specifics

Refer to the documenation for our batch environment to understand how to use PBS on OSC hardware. Some specifics you will need to know to create well-formed batch scripts:

  • All compute nodes on Glenn are 8 cores/processors per node (ppn). Parallel jobs must use ppn=8.
  • If you need more than 24 GB of RAM per node, you will need to run your job on Oakley
  • GPU jobs must request whole nodes (ppn=8) and are allocated two GPUs each.

Using OSC Resources

For more information about how to use OSC resources, please see our guide on batch processing at OSC. For specific information about modules and file storage, please see the Batch Execution Environment page.


Batch Limit Rules

Memory Limit:

It is strongly suggested to consider the memory use to the available per-core memory when users request OSC resources for their jobs. On Glenn, it equates to 3GB/core and 24GB/node.

If your job requests less than a full node ( ppn<8 ), it may be scheduled on a node with other running jobs. In this case, your job is entitled to a memory allocation proportional to the number of cores requested (3GB/ core). For example, without any memory request ( mem=XX ), a job that requests  nodes=1:ppn=1  will be assigned one core and should use no more than 3GB of RAM, a job that requests  nodes=1:ppn=3  will be assigned 3 cores and should use no more than 9GB of RAM, and a job that requests  nodes=1:ppn=8  will be assigned the whole node (8 cores) with 24GB of RAM. It is important to keep in mind that the memory limit ( mem=XX ) you set in PBS does not work the way one might expect it to on Glenn. It does not cause your job to be allocated the requested amount of memory, nor does it limit your job’s memory usage. For example, a job that requests  nodes=1:ppn=1,mem=9GB will be assigned one core (which means you should use no more than 3GB of RAM instead of the requested 9GB of RAM) and you were only charged for one core worth of Resource Units (RU).

A multi-node job ( nodes>1 ) will be assigned the entire nodes with 24GB/node. Jobs requesting more than 24GB/node should be submitted to other clusters (Oakley or Ruby)

To manage and monitor your memory usage, please refer to Out-of-Memory (OOM) or Excessive Memory Usage.

Walltime Limit

Here are the queues available on Glenn:






168 hours



336 hours

Restricted access


96 hours


Job Limit

An individual user can have up to 128 concurrently running jobs and/or up to 2048 processors/cores in use. All the users in a particular group/project can among them have up to 192 concurrently running jobs and/or up to 2048 processors/cores in use. Jobs submitted in excess of these limits are queued but blocked by the scheduler until other jobs exit and free up resources.

A user may have no more than 1000 jobs submitted to both the parallel and serial job queue separately. Jobs submitted in excess of this limit will be rejected.



To cite Glenn, please use the following Archival Resource Key:


Here is the citation in BibTeX format:

ark = {ark:/19495/hpc1ph70},
url = {},
year  = {2009},
author = {Ohio Supercomputer Center},
title = {Glenn supercomputer}

And in EndNote format:

%0 Generic
%T Glenn supercomputer
%A Ohio Supercomputer Center
%R ark:/19495/hpc1ph70
%D 2009

Here is an .ris file to better suit your needs. Please change the import option to .ris.

Documentation Attachment: 

Queues and Reservations

Here are the queues available on Glenn. Please note that you will be routed to the appropriate queue based on your walltime and job size request.

Name Nodes available max walltime max job size notes


Available minus reservations

168 hours

1 node



Available minus reservations

336 hours

1 node

Restricted access


Available minus reservations

96 hours

256 nodes



Entire cluster

48 hours

436 nodes

Restricted access

"Available minus reservations" means all nodes in the cluster currently operational (this will fluctuate slightly), less the reservations listed below. To access one of the restricted queues, please contact OSC Help. Generally, access will only be granted to these queues if performance of the job cannot be improved, and job size cannot be reduced by splitting or checkpointing the job.

In addition, there are a few standing reservations.

Name Times Nodes Available Max Walltime Max job size notes
Debug 8AM-6PM Weekdays 16 1 hour 16 nodes For small interactive and test jobs.
GPU ALL 32 336 hours 32 nodes

Small jobs not requiring GPUs from the serial and parallel queues will backfill on this reservation.

Occasionally, reservations will be created for specific projects that will not be reflected in these tables.