protocol:
{
  "driver": "sheepdog",
  "location": {
    "server": {
      "type": "inet",
      "host": "example.com",
      "port": "1234"
    },
    "vdi": "asdf/i.qcow2"
  },
  "size": 4294967296
}

format:
{
  "driver": "qcow2",
  "file": "0123456789ABCDEF0123456789ABCDE",
  "size": 8589934590
}