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Frequently Asked Questions

Generally speaking, HPC infrastructure is coordinating many discrete units capable of independent computation to cooperate on portions of a task to complete far more computation in a given amount of time than any of the units could do individually. In other words, an HPC system is lots of individual computers working together.

HPC Operations and Information Technology Services (ITS) are separate groups with different responsibilities. ITS will handle issues with your workstation or any other digital device you are issued by NREL. HPC Operations will assist with issues regarding HPC systems. Note that your NREL HPC account is a different account from your ITS credentials that you use to login to your workstation, e-mail, and the many other IT services provided by the Service Desk.
Over the fiscal year, there is a given amount of time each computer in the HPC system(s) can be expected to be operational and capable of performing computation. HPC project allocations allocate a portion of the total assumed available computing time. The sum of all awarded project allocations' compute-time approximates the projected availability of the entire system. Project allocations are identified by a unique "handle" which doubles as a Linux account under which you submit HPC jobs related to the project to the job scheduler. Learn more about requesting an allocation.
OTP tokens are a means of two-factor authentication by combining a temporary (usually lasting 60 seconds) token to use along with your account password. Tokens are generated using the current time stamp and a secure hashing algorithm. Note that you only need an OTP to access systems outside the NREL firewall, namely if you are an external collaborator. NREL employees can be on-site or use a VPN to access HPC systems via the * domain.
VPNs simulate being within a firewall (which is an aggressive filter on inbound network traffic) by encapsulating your traffic in a secure channel that funnels through the NREL network. While connected to a VPN, internal network domains such as * can be accessed without secondary authentication (as the VPN itself counts as a secondary authentication). NREL employees may use the NREL VPN while external collaborators may use the NREL HPC VPN using their OTP token. This provides the convenience of not having to continually type in your current OTP token when accessing multiple systems in a single session.
This is the general term used for any task submitted to the HPC systems to be queued and wait for available resources to be executed. Jobs vary in how computationally intensive they are.
A node is a complete, independent system with its own operating system and resources, much like your laptop or desktop. HPC nodes are typically designed to fit snugly in tight volumes, but in principle you could convert several laptops into a cluster, and they would then be "nodes."
Login nodes are the immediate systems your session is opened on once you successfully authenticate. They serve as preparation systems to stage your user environment and launch jobs. Compute nodes are where your jobs get computed when submitted to the scheduler. You gain exclusive access to compute nodes that are executing your jobs, whereas there are often many users logged into the login nodes at any given time.

As mentioned above, login nodes are often being used by dozens of users at a given time. If you do computationally intensive work on these systems, it will unfairly occupy resources and make the system less responsive for other users. Please reserve your computationally intensive tasks (especially those that will fully utilize CPU cores) for jobs submitted to compute nodes. Offenders of login node abuse will be admonished accordingly. For more information please see our policy on what constitutes inappropriate use.

System time is a regularly occurring interval of time during which NREL HPC systems are taken offline for necessary patches, updates, software installations, and anything else to keep the systems useful, updated, and secure. You will not be able to access the system or submit jobs during system times. System times occur the first Monday every month. A reminder announcement is sent out prior to every system time detailing what changes will take place, and includes an estimate of how long the system time will be. You can check the system status page if you are ever unsure if an NREL HPC system is currently down for system time.
As you become familiar with navigating the HPC Linux systems you may come to prefer to use the same command-line interfaces locally on your workstation to keep your workflow consistent. There are many terminal emulators that can be used on Windows which provide the common Linux and macOS command-line interface. The official Linux command-line emulator for Windows is known as the Windows Subsystem for Linux. Other recommended terminal applications include Git Bash, Git for Windows, Cmder, and MSYS2. Note that PuTTY is not a terminal emulator, it is only an SSH client. The applications listed above implement an ssh command, which mirrors the functionality of PuTTY.
Stated briefly, the SSH protocol establishes an encrypted channel to share various kinds of network traffic. Not to be confused with the ssh terminal command or SSH clients which are applications that implement the SSH protocol in software to create secure connections to remote systems.
Good question! There may be hundreds of reasons why. Please contact HPC Support with a message containing as many relevant details as you can provide so we are more likely to be able to offer useful guidance (such as what software you're using, how you are submitting your job, what sort of data you are using, how you are setting up your software environment, etc.).