Define a Mapping for Percentage or Bytes (GB,MB) in Kibana

Thanks for the reply @nickpeihl but I do not find edit option once when an index is created can u be a little bit more specific.

{
  "index_patterns": "diskusage-*",
  "mappings": {
      "properties": {
        "created_at": {
          "type": "date",
          "format": "yyyy-MM-dd HH:mm:ss||yyyy-MM-dd||epoch_millis"
        },
        "disk_usage":{
          "type":"float"
        }
  },
  "settings": {
    "number_of_shards": 2,
    "number_of_replicas": 1
  },
  "aliases": {
    "diskusage": {}
  }
}
}

Will this work for me! or do I have to provide a format too.

I saw the advance index setting option: