Configuring RAID 1 on Leap Micro 6.0 via Ignition/Combustion

[bartk]

I’m currently trying to set up openSUSE Leap Micro. Version 6.0 no longer comes with a traditional installer, so I have to do this via Ignition file.
I found some examples in both Ignition[1] and Butane[2] docs, but I’m still encountering issues. I am trying first on a virtual machine (KVM host) with two virtual disks with an custom ISO-Image mounted.
The self-install image contains jeos-firstboot, but it doesn’t support install on two disks, so I am not sure which media choose.

1. Example Configs | Ignition
2. Examples | Butane

my current butane config

variant: fcos
version: 1.3.0
boot_device:
  mirror:
    devices:
      - /dev/sda
      - /dev/sdb
storage:
  disks:
    - device: /dev/sda
      partitions:
        - label: root-1
          size_mib: 10240
        - label: var-1
    - device: /dev/sdb
      partitions:
        - label: root-2
          size_mib: 10240
        - label: var-2
  raid:
    - name: md-var
      level: raid1
      devices:
        - /dev/disk/by-partlabel/var-1
        - /dev/disk/by-partlabel/var-2
  filesystems:
    - device: /dev/md/md-var
      path: /var
      format: xfs
      wipe_filesystem: true
      with_mount_unit: true
  files:
    - path: /etc/hostname
      mode: 0644
      overwrite: true
      contents:
        inline: "kubic-1"

(there is no tag leapmicro-60 so I picked -53)