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Warning!

Puhti and Mahti will be decommissioned after Roihu becomes available. Users should clean up unnecessary files and move any required data by the end of August 2026. See the Roihu data preparation instructions for details.

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 preliminary information about CSC's next national supercomputer Roihu, which is projected to be in researchers' use in spring 2026. Please note that the details may evolve over time. See tentative schedule 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 A fill:#dceeceff;

Roihu will be 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 one month after the general availability of Roihu, but earliest by 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 August 2026. CSC will publish a detailed Roihu migration guide after Roihu's general availability.

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 will have 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 will 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 will have 768 GiB of memory, while the remaining 72 nodes will have an extended memory of 1 536 GiB each.

Each GPU node will be 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 with 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 gives a total of 528 GPUs and 38 016 CPU cores in the whole GPU partition.

The system will also provide 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

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 will be Red Hat Enterprise Linux 9 (RHEL9).

Storage

Parallel file system

Roihu will have 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 will ensure responsiveness of Home and ProjAppl even under heavy Scratch usage.

The Scratch disk of Roihu will be 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 will 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 we will introduce a new disk area called ProjData. ProjData 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 will have a small 960 GB local disk suitable for storing temporary files during jobs. High-performance local storage will be available on the high-memory and visualization nodes, each of which will include 2 x 7.68 TB fast NVMe disks.

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

Network

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

Software and programming environment

We intend to provide a comprehensive stack of pre-installed HPC libraries and scientific software on Roihu similar to Puhti and Mahti. Some older and less used software and software 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. More information will be included in the migration guide.

The programming environment of Roihu will otherwise be similar to Mahti, including e.g.

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

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

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 – coming in spring 2026!