To view free disk space in ElasticSearch machines use any of following url:
$ curl "http://host1:9200/_cat/nodes?h=h,diskAvail"
Output:
host1 25.7gb
host2 25.1gb
host3 24.5gb
If you need output in json format use following command:
$ curl "http://me31:9200/_nodes/stats/fs?pretty=1"