Comment 3 for bug 1932976

I'm missing the storage config you're trying to process. IIUC, our existing preserve: true raid scenario looks like this (see curtin/examples/tests/preserve-raid.yaml) but let's extend it and create a partition on the raid

- type: disk
  id: sda
  preserve: true
- type: disk
  id: sdb
  preserve: true
- type: raid
  id: raid-md1
  raidlevel: raid1
  devices: [sda, sdb]
  preserve: true
- type: partition
  id raid1-md1-part1
  device: raid-md1
  size: 1G
- type: format
 ....

The disk handler never runs against a raid device, just like it doesn't run against lvm or any other composed device.

I think if you extend the existing preserve-raid vmtest to create a different partition layout but keep the raid mirror; that should just work and if not we'll see the traceback on where it failed.