Provisioning disks

As a tech preview, Warewulf provides structures to define disks, partitions, and file systems. These structures can generate a configuration for Ignition to provision partitions and file systems dynamically on cluster nodes.

Ignition can, for example, create swap partitions or /scratch file systems.

Note

Warewulf is not currently able to provision the node image onto an explicitly provisioned root file system.

Requirements

Partition and file system creation requires both ignition and sgdisk to be installed in the image.

Rocky Linux

dnf install ignition gdisk

Note

Packages for Ignition are not currently available for Rocky Linux 8, but it is available for Rocky Linux 9 as part of “appstream.”

openSuse Leap

zypper install ignition gptfdisk

Disks and partitions

A node or profile can have several disks. Each disk is identified by the path to its block device. Each disk holds a map to its partitions and a bool switch to indicate if an existing, non-matching partition table should be overwritten.

Each partition is identified by its label. The partition number can be omitted, but specifying it is recommended as Ignition may fail without it. Partition sizes should also be set (specified in MiB), except for the last partition: if no size is given, the maximum available size is used. Each partition has the switches should_exist and wipe_partition_entry which control the partition creation process. When omitting a partition number the wipe_partition_entry should be true, as this allows ignition to replace the existing partition.

wwctl node set n1 \
  --diskname /dev/vda --diskwipe \
  --partname scratch --partcreate --partnumber 1

File systems

File systems are identified by their underlying block device, preferably using the /dev/by-partlabel format. Except for a swap partition, an absolute path for the mount point must be specified for each file system. Depending on the image used, valid formats are btrfs, ext3, ext4, and xfs. Each file system has the switch wipe_filesystem to control whether an existing file system is wiped.

wwctl node set n1 \
  --diskname /dev/vda --partname scratch \
  --fsname scratch --fsformat btrfs --fspath /scratch

Boot-time configuration

Ignition uses systemd, as the underlying sgdisk command relies on dbus notifications.

  1. ignition-disks-ww4.service uses Ignition to create the specified partitions and file systems.

  2. ww4-disks.target depends on a matching .mount unit for each mounted file system.

  3. Each .mount creates the necessary mount points in the root file system and mounts the provisioned file systems during boot.

These services and mount units are generated by the ignition overlay and depend on the existence of the file /warewulf/ignition.json, also generated by the ignition overlay.

Example disk configurations

This command formats a btrfs file system on a “scratch” partion of “vda” and mounts it at /scratch.

wwctl node set n1 \
  --diskname /dev/vda --diskwipe \
  --partname scratch --partcreate --partnumber 1 \
  --fsname scratch --fsformat btrfs --fspath /scratch

This command adds a swap partition to the “vda” disk.

wwctl node set n1 \
  --diskname /dev/vda \
  --partname swap --partsize=1024 --partnumber 2 \
  --fsname swap --fsformat swap --fspath swap

Re-using or wiping disks

For empty disks the desired configuration is created and the filesystems are mounted. If partitions or file systems already exist on the disk, ignition tries to reuse existing file systems by default.

To ignore existing file systems and provision fresh file systems on each boot, specify the --fswipe` flag for that filesystem, and --diskwipe for the disk, as necessary.

If you would like to re-use existing partitions but want to replace existing file systems once, you may

  • wipe the existing data with tools like wipefs or dd [1]; or

  • set the --fswipe flag and remove it after one reboot.

See the upstream ignition documentation for additional information.