------Brief introduction to HPC environments {.title}
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Notes on vocabulary
- You can roughly think that one **node** is a single computer
- A node on a supercomputer contains:
- One or more central processing units (**CPUs**) with many **cores**
- Shared **memory**
- Some nodes may also have:
- **Local storage** (NVMe)
- Graphics processing units (**GPUs**)
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Cluster systems
- Login nodes are used to set up jobs (and to launch them)
- Jobs are run on the compute nodes
- A batch job system (scheduler) is used to run and manage the jobs
- On CSC machines, we use **Slurm**
- Note: Slurm uses term CPU for cores, which is a bit confusing
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Available HPC and cloud resources
Puhti is the general-purpose supercomputer ☑️
Mahti is the massively parallel flagship supercomputer
LUMI is a European pre-exascale supercomputer operated by CSC
Pouta provides cloud resources via OpenStack (IaaS)
Rahti provides containers via OKD (PaaS)
Allas provides object storage for all services
Which supercomputer to use?
What kind of resources can your application use?
Can it use more than one core?
How much memory will it need?
Can it use a GPU or an NVMe?
What takes long (i.e., the time-limiting part) in your job?
See what kind of resources are available?
Is my code already installed?
Max runtime, partitions (queues), provisioning policy (Per core/per node/other)
Each system is different, so check the documentation
Quick and dirty comparison of Puhti, Mahti and LUMI
| Puhti | Mahti | LUMI | |
|---|---|---|---|
| Pre-installed apps | 120+ | 40+ | See here |
| Cores per node | 40 | 128 | 128 |
| Job size (min-max cores) | 1-1040 | 1-25600 | 1-65536 |
| Memory per node (GiB) | 192-1536 | 256 | 256-1024 |
| GPU cards | 320 (V100) | 96 (A100) | 11912 (MI250X) |
| Nodes with NVMe (CPU+GPU) | 106+80 | 60+24 | 8+8 |
In short: Mahti is for large parallel jobs, prepare to install and optimize your code. Still, one Puhti *node* is 10x your laptop. LUMI is like Mahti + massive AMD GPU capacity