---
title: Accessing Slurm Cluster
#tags:
#keywords:
last_updated: 13 June 2019
#summary: ""
sidebar: merlin6_sidebar
permalink: /merlin6/slurm-access.html
---

## The Merlin6 Slurm batch system

Clusters at PSI use the [Slurm Workload Manager](http://slurm.schedmd.com/) as the batch system technology for managing and scheduling jobs.
Historically, *Merlin4* and *Merlin5* also used Slurm. In the same way, **Merlin6** has been also configured with this batch system.

Slurm has been installed in a **multi-clustered** configuration, allowing to integrate multiple clusters in the same batch system.
* Two different Slurm clusters exist: **merlin5** and **merlin6**.
   * **merlin5** is a cluster with very old hardware (out-of-warranty).
   * **merlin5** will exist as long as hardware incidents are soft and easy to repair/fix (i.e. hard disk replacement)
   * **merlin6** is the default cluster when submitting jobs.

This document is mostly focused on the **merlin6** cluster. Details for **merlin5** are not shown here, and only basic access and recent
changes will be explained (**[Official Merlin5 User Guide](https://intranet.psi.ch/PSI_HPC/Merlin5)** is still valid).

### Merlin6 Slurm Configuration Details

For understanding the Slurm configuration setup in the cluster, sometimes can be useful to check the following files:

* ``/etc/slurm/slurm.conf`` - can be found in the login nodes and computing nodes.
* ``/etc/slurm/cgroup.conf`` - can be found in the computing nodes, is also propagated to login nodes for user read access.
* ``/etc/slurm/gres.conf`` - can be found in the GPU nodes, is also propgated to login nodes and computing nodes for user read access.

The previous configuration files can be found in the *login nodes* correspond exclusively to the **merlin6** cluster configuration files. These
configuration files are also present in the **merlin6** *computing nodes*.

Slurm configuration files for the old **merlin5** cluster have to be directly checked on any of the **merlin5** *computing nodes*: those files *do
not* exist in the **merlin6** *login nodes*.

### Merlin5 Access

Keeping the **merlin5** cluster will allow running jobs in the old computing nodes until users have fully migrated their codes to the new cluster.

From July 2019, **merlin6** becomes the **default cluster** and any job submitted to Slurm will be submitted to that cluster.
However, users can keep submitting to the old **merlin5** computing nodes by using the option ``--cluster=merlin5`` and using the corresponding
Slurm partition with ``--partition=merlin``. In example:

```bash
srun --clusters=merlin5 --partition=merlin hostname
sbatch --clusters=merlin5 --partition=merlin myScript.batch
```

---

## Using Slurm 'merlin6' cluster

Basic usage for the **merlin6** cluster will be detailed here. For advanced usage, please use the following document [LINK TO SLURM ADVANCED CONFIG]()

### Merlin6 Node definition

The following table show default and maximum resources that can be used per node:

| Nodes                              | Def.#CPUs | Max.#CPUs | Def.Mem/CPU | Max.Mem/CPU | Max.Mem/Node | Max.Swap | Def.#GPUs | Max.#GPUs |
|:---------------------------------- | ---------:| ---------:| -----------:| -----------:| ------------:| --------:| --------- | --------- |
| merlin-c-[001-022,101-122,201-222] | 1 core    | 44 cores  | 8000        | 352000      | 352000       | 10000    | N/A       | N/A       |
| merlin-g-[001]                     | 1 core    | 8 cores   | 8000        | 102498      | 102498       | 10000    | 1         | 2         |
| merlin-g-[002-009]                 | 1 core    | 10 cores  | 8000        | 102498      | 102498       | 10000    | 1         | 4         |

If nothing is specified, by default each core will use up to 8GB of memory. More memory per core can be specified with the ``--mem=<memory>`` option,
and maximum memory allowed is ``Max.Mem/Node``.

In *Merlin6*, memory is considered a Consumable Resource, as well as the CPU.

### Merlin6 Slurm partitions

Partition can be specified when submitting a job with the ``--partition=<partitionname>`` option.
The following *partitions* (also known as *queues*) are configured in Slurm:

| Partition   | Default Partition | Default Time | Max Time | Max Nodes | Priority |
|:----------- | ----------------- | ------------ | -------- | --------- | -------- |
| **general** | true              | 1 day        | 1 week   | 50        | low      |
| **daily**   | false             | 1 day        | 1 day    | 60        | medium   |
| **hourly**  | false             | 1 hour       | 1 hour   | unlimited | highest  |

General is the *default*, so when nothing is specified job will be by default assigned to that partition. General can not have more than 50 nodes
running jobs. For **daily** this limitation is extended to 60 nodes while for **hourly** there are no limits. Shorter jobs have more priority than
longer jobs, hence in general terms would be scheduled before (however, other factors such like user fair share value can affect to this decision).

### Merlin6 User limits

By default, users can not use more than 528 cores at the same time (Max CPU per user). This limit applies for the **general**  and **daily** partitions. For the **hourly** partition, there is no restriction.
These limits are softed for the **daily** partition during non working hours and during the weekend as follows:

| Partition   | Mon-Fri 08h-18h | Sun-Thu 18h-0h | From Fri 18h to Sun 8h  | From Sun 8h to Mon 18h |
|:----------- | --------------- | -------------- | ----------------------- | ---------------------- |
| **general** | 528             | 528            | 528                     | 528                    |
| **daily**   | 528             | 792            | Unlimited               | 792                    |
| **hourly**  | Unlimited       | Unlimited      | Unlimited               | Unlimited              |