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Warning!

Puhti and Mahti are being decommissioned in stages, and their storage areas will become fully unavailable from 15 October 2026. Clean up unnecessary files and move any data you need to keep by 31 August 2026. See the Roihu data migration guide for instructions on transferring your data to Roihu.

Puhti scratch is very full: keep only active data there and move or delete everything else. No new Puhti scratch quota will be granted.

Roihu supercomputer

Note

This page contains information about CSC's next national supercomputer Roihu, which is now available for researchers.

As part of the transition, Mahti and Puhti will be decommissioned in steps over summer and fall 2026. See the schedule for Mahti and Puhti shutdown below.

Schedule

graph LR;
    A{{"<b>September 2025</b>
        Roihu installation
        in progress"}} --> B;
    B{{"<b>April 2026</b>
        Pilot phase
        starts"}} --> C;
    C{{"<b>June 2026</b>
        Roihu general
        availability (GA)"}} --> D;
    D{{"<b>End of July 2026</b>
        Puhti <i>computing
        services</i> shut down"}} --> E;
    E{{"<b>End of August 2026</b>
        Mahti <i>computing
        services</i> shut down"}} --> F;
    F{{"<b>Mid October 2026</b>
        Puhti <i>storage
        services</i> shut down"}} --> G;
    G{{"<b>Mid October 2026</b>
        Mahti <i>storage services</i>
        shut down"}}
    style C fill:#dceeceff;

Roihu is installed in the same datacenter as LUMI, meaning that the system will be brought up without disrupting Puhti and Mahti services. There will also be a margin between Roihu general availability and the decommissioning of Puhti and Mahti to enable users to migrate to Roihu without a break in HPC access.

Puhti will be decommissioned in two stages: First, Puhti's computing services will be shut down 31 July 2026 at 12:00 EEST. This means that jobs will not run after this date on Puhti anymore. Puhti's storage and login nodes will, however, remain accessible until midday October 15th 2026, after which Puhti will be retired completely.

Mahti will be closed in a similar two-stage process. Mahti’s computing services will be shut down on 31 August 2026 at 12:00 EEST, and jobs will not run on Mahti after this date. Its storage and login nodes will remain accessible until midday 15 October 2026, after which Mahti will be retired completely.

Between September and October 2026, the storage services will not be covered by service contracts. As a result, we cannot guarantee that they will remain accessible throughout this period. We strongly encourage all users to prioritize moving their data by the end of August 2026.

Prepare for data migration from Mahti and Puhti to Roihu

If you have any data that you need to migrate from Puhti to Roihu, please be prepared to do it during summer 2026, aiming to complete it by the end of August. See the Roihu migration guide on how you can transfer data directly from Mahti and Puhti to Roihu.

If you cannot move data directly from Mahti or Puhti to Roihu between early July and end of August, consider using Allas or LUMI-O for short-term data storage.

For any questions and concerns regarding transferring data between the systems, feel free to contact the CSC service desk, or attend CSC's weekly user support coffee breaks.

Compute

Roihu has a total of 486 CPU nodes and 132 GPU nodes. The high-performance LINPACK (HPL) performance is estimated to be 10.5 PFlop/s for the CPU nodes and 23.4 PFlop/s for the GPU nodes, resulting in an aggregate HPL performance of 33.9 PFlop/s for the full system.

The CPU nodes have two 192-core AMD Turin 9965 CPUs each, amounting to 186 624 CPU cores altogether. The CPUs are based on the AMD Zen 5 architecture, which supports the AVX-512 vector instruction set. 414 of the CPU nodes have 768 GiB of memory, while the remaining 72 nodes have an extended memory of 1 536 GiB each.

Each GPU node is equipped with 4 Nvidia GH200 Grace Hopper superchips. Each GH200 superchip comprises one Hopper (H100) GPU and one Grace CPU with 72 ARM CPU cores, which are connected via a very fast interface. Each GH200 superchip has 120 GiB CPU memory and 96 GiB GPU memory, providing a total of 480 GiB CPU memory per node. This results in a total of 528 GPUs and 38 016 CPU cores in the whole GPU partition.

The system also provides four visualization nodes with two Nvidia L40 GPUs each, as well as four high-memory CPU nodes with 6 TiB memory and higher single-thread performance.

Nodes

Node names

The node names below describe the different node types in Roihu. Batch job partitions and allocation types in Slurm may use different names. See the Slurm partition documentation for how to request these resources in Slurm.

Name Number of nodes Compute Cores Memory (GiB) Local disk (TB)
M 414 AMD Turin 9965 2 x 192 cores (x86) @ 2.25 GHz 768 0.96
L 72 AMD Turin 9965 2 x 192 cores (x86) @ 2.25 GHz 1536 0.96
XL 4 AMD Turin 9555 2 x 64 cores (x86) @ 3.20 GHz 6144 15.36
V 4 AMD Turin 9335
Nvidia L40		 2 x 32 cores (x86) @ 3.40 GHz
2 x GPUs		 384
2 x 48		 15.36
GPU 132 Nvidia GH200 4 x 72 cores (ARM)
4 x GPUs		 4 x 120
4 x 96		 0.96

The operating system of Roihu is Red Hat Enterprise Linux 9 (RHEL9).

Storage

Parallel file system

Roihu has two independent flash-based DDN EXAScaler Lustre file systems – a 6.0 PiB Scratch space and a 0.5 PiB storage system for project applications and users' personal Home directories. Separate file systems ensure responsiveness of Home and ProjAppl even under heavy Scratch usage.

The Scratch disk of Roihu is more than ten times as performant as Puhti Scratch. Specifically, the peak I/O performance of Roihu Scratch is expected to be around 560 GB/s for read and 280 GB/s for write. The Home and ProjAppl disk areas are expected to have read and write bandwidths of 120 GB/s and 100 GB/s, respectively.

Similar to Puhti, Roihu Scratch disk will be regularly cleaned of files that have not been accessed in the last 180 days to avoid inactive data accumulating on the system. For longer-term storage and sharing of datasets between multiple projects, we will introduce a new disk area called Dataset. Dataset access and quota will be applied for and managed in MyCSC, and the disk area will have its own billing model.

Local storage capacity

Each Roihu CPU and GPU node have a small 960 GB local disk suitable for storing temporary files during jobs. High-performance local storage is available on the high-memory (XL) and visualization (VIZ) nodes, where each node includes a total of 13 TiB of fast NVMe disks.

The available storage quota that a single user can access in their jobs depends on the system partition they use:

Allocation type Quota per user
R (shared nodes) 20 GiB
N (full nodes) 600 GiB
G (GPU nodes) 150 GiB
Hugemem (XL) nodes 1.6 TiB
V (visualization nodes) 6.5 TiB

As a new feature, users can also request local disk mounts from a centralized pool of fast storage resources. This fast storage capacity is provided over the network and will appear as local scratch storage from within a Slurm job. The total capacity of the disaggregated NVMe resource is 307.2 TB.

Network

The network of Roihu is based on an InfiniBand NDR interconnect. Each CPU node is connected to the network with one 200 Gb/s link, while in the GPU partition there are four 200 Gb/s links per node, one per GPU.

Software and programming environment

We intend to provide a comprehensive stack of pre-installed HPC libraries and scientific software on Roihu, similar to those on Puhti and Mahti. Some older and less used software packages and versions may, however, be deprecated. Please also note that any software compiled on Puhti and Mahti will most likely need to be recompiled on Roihu. Instructions for installing applications are provided in the getting started with Roihu tutorial

The programming environment of Roihu is otherwise similar to Mahti, including:

  • The GNU compiler stack
  • The AOCC compiler stack
  • CUDA and NVIDIA HPC Software Development Kit (SDK)
  • OpenMPI as the main MPI library

Like Puhti and Mahti, Roihu also features a web interface for easy-to-use interactive access and running graphical user interfaces.

A list of currently supported applications on Roihu can be found on the applications page.

Sensitive data services in Roihu

CSC supercomputers, including Roihu, are maintained according to the best practices of HPC management: processes are planned and documented, systems are constantly monitored, and security patches are applied without delay. Further, all users log in using two-factor authentication. Thus, these environments are quite secure by default. However, CSC can't guarantee that there is no risk of a data breach, as new security incidents emerge from time to time.

For use cases that require higher security, Roihu is being developed to support workflows that require enhanced controls for handling sensitive and confidential data. Roihu will introduce dedicated capabilities for regulated data workflows.

The sensitive data capability will be introduced after Roihu's initial availability. Pilot use of the sensitive computing environment is currently estimated to begin in autumn 2026, with general availability potentially following in early 2027, depending on the results and experiences from the pilot phase.

The user workflow is expected to resemble CSC’s current Sensitive Data Desktop to HPC job submission model, where sensitive data jobs are submitted from a secure environment (SD Desktop) and input/output data are handled through protected data services (SD Connect). The jobs will be executed in job-specific isolated environments that will not be able to access the internet or the shared disk areas of Roihu.

Read more about the sensitive data services at CSC.

More information

Roihu supercomputer – now available for use!