Overview of disk areas

• Main disk areas and their specific uses on Puhti and Mahti
  • See here for information about the disk areas on LUMI
• Moving data between supercomputers
• Understanding quotas (available space and number of files) of different disk areas
• Additional fast disk areas

Disk and storage overview

Main disk areas in Puhti/Mahti

• Home directory ($HOME)
  • Other users cannot access your home directory
• ProjAppl directory (/projappl/project_name)
  • Shared with project members
  • Possible to limit access (chmod g-rw) to subfolders
• Scratch directory (/scratch/project_name)
  • Shared with project members
  • Files older than 180 days will be automatically removed
• These directories reside on the Lustre parallel file system
• Default quotas and more info in disk areas section of Docs CSC

Moving data between and to/from supercomputers

• Puhti and Mahti have separate file systems
• Data can be moved between the supercomputers
  • directly with rsync
  • via Allas object storage
• There are many ways to transfer data between the CSC supercomputers and your local computer

Displaying current status of disk areas

• Use the csc-workspaces command to show available projects and quotas

Disk and storage overview (revisited)

Additional fast local disk areas

• $TMPDIR on login nodes
  • Each of the login nodes have 2900 GiB of fast local storage in $TMPDIR
  • The local disk is meant for temporary storage (e.g. compiling software) and is cleaned frequently
• NVMe disks on some compute nodes on Puhti
  • Interactive, I/O and GPU nodes have fast local disks (NVMe) in $LOCAL_SCRATCH
  • Also, the GPU nodes on Mahti have fast local storage available
  • You must copy data to and from the fast disk during your batch job since the NVMe is accessible only during your job allocation
  • If your job reads and/or writes a lot of small files, using this can give a huge performance boost!

What are the different disk areas for?

• Allas – for data which is not actively used
• $HOME – small, only for the most important (small) files, personal access only
• /scratch – main working area, shared with project members, only for data in active use
• /projappl – not cleaned up, e.g. for shared binaries
• Login node $TMPDIR – compiling, temporary storage, fast I/O
• Compute node NVMe $LOCAL_SCRATCH – fast I/O in batch jobs

Best practices

• None of the disk areas are automatically backed up by CSC, so make sure to perform regular backups to, e.g., Allas
• Don’t run databases or Conda on Lustre (/projappl, /scratch, $HOME)
  • Containerize Conda environments with Tykky and use other CSC services like Kaivos or cPouta for databases (Rahti also an option but connecting to it from Puhti/Mahti is complicated)
• Don’t create a lot of files, especially within a single folder
  • If you’re creating 10 000+ files, you should probably rethink your workflow
• Consider using fast local disks when working with many small files
• Lustre best practices and efficient I/O in high-throughput workflows