overlay-gizmo/scripts/disk_layout.json

{
  "_comment": "See http://www.chromium.org/chromium-os/building-chromium-os/disk-layout-format",
  "metadata":{
    "rootdev_base": "/sys/devices/pci0000:00/0000:00:1f.2/ata1/host*/target*/*/block/sd*"
  },
  "parent": "legacy_disk_layout.json",
  "layouts":{
    "common":[
      {
        "num": 3,
        "size":"400 MiB",
        "fs_size":"350 MiB"
      },
      {
        "num": 1,
        "size":"400 MiB"
      }
    ],
    "base":[
      {
        "num": 5,
        "size":"400 MiB"
      }
    ],
    "usb":[
      {
        "num": 5,
        "size":"2 MiB"
      }
    ]
  }
}