Introduction to High Performance and High Throughput Computing



Legion Scheduler

  • Tries to give each user an equal share of the machine at any given moment
  • Tries to fill gaps with small, short jobs
  • Has a few special sets of nodes to run test (short, small) or interactive jobs


Anything that uses:

  • a lot of CPU time
  • a lot of RAM
  • a lot of disk access

Production work should be run as a job.

What Can Run

We can provide (stable) application centrally, and compile up software to put in the /shared/ucl/apps space.

You're free to run almost anything that you can build on Legion, though.

Some departments also provide applications, e.g. Chemistry Department: module load chemistry-modules.

We reserve the right to ban the use of applications that prevent or harm other users' use of the cluster.


Time Cores Queue Type
≤ 15 mins ≤1 node Rapid Test Queue
≤ 1 day ≤ 512 cores Large Parallel Queue
≤ 2 days ≤ 256 cores Smaller Parallel Queue
≤ 3 days 1 core Serial Queue

(Actually more complex than this, check the website.)

Extraordinary Resource Requests

Data Policies


  • Legion is not a long-term data repository
  • Do not store the only copy of your data on Legion


Legion is not suitable for Highly Restricted data and above.

Level Examples
Secret: Identifiable patient information
... Personal financial details
... Confidential investigations
Highly Restricted: Student profiles
... Unpublished commercially sensitive material
Restricted: UCL main web page
... Unpublished research data
Normal: Email about fridge-cleaning meeting

(See: UCL's data security policy)


Responsibility for the accuracy of the results of software installed or available on Legion is the sole responsibility of researchers.


  • Test your software
  • Check your results


  • ssh is the only recommended method to connect to/from Legion
  • UCL is not responsible for security of non-UCL machines
  • Ensure your machines are reasonably secure


  • Home directories have a 50 GB quota
  • Scratch has a 200 GB quota
    • However you can use as much as you want for up to two weeks
    • After two weeks job submission is disabled until you decrease usage to below quota
  • If you need more, we can make small increases (up to double)
    • For more apply to the CRAG

Support Queries

A Good Ticket

Tell us:

  • What you're trying to do (technical)
  • Exact error output
  • Job IDs, scripts, and relevant file paths
  • Whether we can look at your files

Keeping Tickets Sane

Subject: Re: Error When Compiling My_App v0.45 (Ref:IN:01287844)

Keeping one ticket ID per problem helps us immensely.

Other Compute Resources

UCL Funded

  • Emerald
    • for GPU jobs
  • Departmental clusters
    • talk to your local IT manager


  • DIRAC collection
  • US National Labs
  • EGI
  • (Cloud Providers)