Preparing compute nodes for eessi

Last updated on 2026-06-17 | Edit this page

Overview

Questions

  • What is a loop device and when is it needed?
  • How do you create persistent storage for a diskless compute node?

Objectives

  • Create a large file with dd to act as a virtual disk
  • Map the file to a loop device using losetup
  • Partition and format the loop device
  • Mount the loop device for use by EESSI

Credit to: https://linuxconfig.org/how-to-create-loop-devices-on-linux

To use eessi on diskless compute nodes, we need to create “pseudo” disk using

  • dd for creating an empty file, the size of the disk we need.
  • losetup
  • parted
  • mkfs.ext4
  • mount

Create file

dd if=/dev/zero of=loopdevice bs=1M count=32768

Map the file to a block device

Determine the next available block device:
sudo losetup -f
Map the file called loopdevice to the next available block device:
sudo losetup -f loopdevice

Create a partition and filesystem

  • sudo parted -s /dev/loop0 mklabel msdos
  • sudo parted -s /dev/loop0 mkpart primary 0% 100%
  • sudo mkfs.ext4 /dev/loop0p1

Mount the file as a drive

  • sudo mount /dev/loop0 /cvmfs
Key Points
  • Loop devices map regular files to block devices, allowing them to be partitioned and mounted like physical disks
  • This provides EESSI with a mountable filesystem at /cvmfs on diskless compute nodes