# Introduction

![Merlin](../../images/merlin_cave.png){ width="400px" }
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_Within his lair, the wizard ever strives for the perfection of his art._
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## About Merlin7

PSI's Merlin7 cluster is run on top of an IaaS (Infrastructure as a Service) *vCluster* on the [CSCS Alps infrastructure](https://www.cscs.ch/computers/alps). It is fully integrated with the PSI service landscape was designed to provide the same end user experience as its PSI-local predecessor clusters.

Merlin7 has been in **production** since beginning of June 2025. 

All PSI users can request access to Merlin7, please go to the [Requesting Merlin Accounts](requesting-accounts.md) page and complete the steps given there.

In case you identify errors or missing information, please provide feedback through [merlin-admins mailing list](mailto:merlin-admins@lists.psi.ch) mailing list or [submit a ticket using the PSI service portal](https://psi.service-now.com/psisp).

## Infrastructure

### Hardware

The Merlin7 cluster contains the following node specification:

| Node     | #N | CPU                                             | RAM             | GPU         | #GPUs |
| ----:    | -- | ---                                             | ---             | ----:       | ---:  |
| Login    |  2 | 2 AMD EPYC 7742 (64 Cores 2.25GHz)              | 512GB           |             |       |
| CPU      | 77 | 2 AMD EPYC 7742 (64 Cores 2.25GHz)              | 512GB           |             |       |
| GPU A100 |  8 | 2 AMD EPYC 7713 (64 Cores 3.2GHz)               | 512GB           | A100 80GB   |     4 |
| GPU GH   |  5 | NVIDIA ARM Grace Neoverse v2 (144 Cores 3.1GHz) | 864GB (Unified) | GH200 120GB |     4 |

### Network

The Merlin7 cluster builds on top of HPE/Cray technologies, including a high-performance network fabric called Slingshot. This network fabric is able
to provide up to 200 Gbit/s throughput between nodes. Further information on Slignshot can be found on at [HPE](https://www.hpe.com/psnow/doc/PSN1012904596HREN).

Through software interfaces like [libFabric](https://ofiwg.github.io/libfabric/) (which available on Merlin7), application can leverage the network seamlessly.

### Storage

Unlike previous iteration of the Merlin HPC clusters, Merlin7 _does not_ have any local storage. Instead storage for the entire cluster is provided through
a dedicated storage appliance from HPE/Cray called [ClusterStor](https://www.hpe.com/psnow/doc/PSN1012842049INEN.pdf).

The appliance is built of several storage servers:

* 2 management nodes
* 2 MDS servers, 12 drives per server, 2.9TiB (Raid10)
* 8 OSS-D servers, 106 drives per server, 14.5 T.B HDDs (Gridraid / Raid6)
* 4 OSS-F servers, 12 drives per server 7TiB SSDs (Raid10)

With effective storage capacity of:

* 10 PB HDD
    * value visible on linux: HDD 9302.4 TiB
* 162 TB SSD
    * value visible on linux: SSD 151.6 TiB
* 23.6 TiB on Metadata

The storage is directly connected to the cluster (and each individual node) through the Slingshot NIC.