Disk Management

Warewulf itself does not manage disks, partitions, or file systems directly, but provides structures in the configuration for these objects. At the moment warewulf supports ignition to create the partitions and file systems.

Note

It is not currently possible to manage the root file system with Warewulf.

Warewulf can be used, for example, to create swap partitions or /scratch file systems.

Requirements

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

Storage objects

The format of the storage objects is inspired by butane/ignition; but, where butane/ignition uses lists for holding disks, partitions and file systems, Warewulf uses maps instead.

A node or profile can have several disks, where each disk is identified by the path to its block device. Every disks holds a map to its partitions and a bool switch to indicate if an existing partition table should be overwritten if it does not matched the desired configuration.

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 of 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.

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 container 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.

Ignition Implementation

The ignition implementation uses systemd services, as the underlying sgdisk command relies on dbus notifications. All necessary services are distributed by the ignition overlay and depends on the existence of the file /warewulf/ignition.json. This file is created by the template function {{ createIgnitionJson }} only if the configuration contains necessary specifications for disks, partitions, and file systems. If the file /warewulf/ignition.json exists, the service ignition-disks-ww4.service calls the ignition binary which takes creates partitions and file systems. A systemd .mount unit is created for each configured file system, which also creates the necessary mount points in the root file system. These mount units are required by the enabled ww4-disks.target. Entries in /etc/fstab are created with the no_auto option so that file systems can be easily mounted.

Example disk configuration

The following command will create a /scratch file system on the node n01.

wwctl node set n01 \
  --diskname /dev/vda --diskwipe \
  --partname scratch --partcreate --partnumber 1 \
  --fsname scratch --fsformat btrfs --fspath /scratch

As this is a single file system, the partition number can be omitted.

A swap partition with 1Gig can be added with

wwctl node set n01 \
  --diskname /dev/vda \
  --partname swap --partsize=1024 --partnumber 2 \
  --fsname swap --fsformat swap --fspath swap

which has the partition number 1 so that it will be added before the /scratch partition.

Wiping disks

Unless you specify the –fswipe flag for a filesystem, ignition will try to reuse existing file systems. For empty disks this means that the desired configuration is created and the filesystems are mounted; and so the –fswipe can be omitted so data is on the disk isn’t wiped. If there are pre-existing partitions and filesystem on the disk, omitting the –fswipe may lead to the outcome that no filesystems are created and mounted. In that case you should: * wipe the existing data with the means of tools like wipefs or dd [1] * set the –fswipe flag and remove it after one reboot, if you want to keep existing data on the disk.

[1]

With wipefs you have to remove the filesystem and parition information. E.g. use wipefs -fa /dev/vda* to remove all filesystem information and partition information.

See also ignition documentation for additional information.

Troubleshooting

If the partition creation didn’t work as expected you have a few options to investigate:

• Add systemd.log_level=debug and or rd.debug to the kernelArgs of the node you’re working on.

• After the next boot you should be able to find verbose information on the node with journalctl -u ignition-ww4-disks.service.

• You could also check the content of /warewulf/ignition.json.

• You could try to tinker with /warewulf/ignition.json calling

  /usr/lib/dracut/modules.d/30ignition/ignition \
    --platform=metal \
    --stage=disks \
    --config-cache=/warewulf/ignition.json \
    --log-to-stdout
  

  after each iteration on the node directly until you find the settings you need. (Make sure to unmount all partitions if ignition was partially successful.)

• Sometimes you need to add should_exist: "true" for the swap partition as well.