How to disable ElasticSearch disk quota / watermark

In its default configuration, ElasticSearch will not allocate any more disk space when more than 90% of the disk are used overall (i.e. by ElasticSearch or other applications).

You can set the watermark extremely low using

curl -X PUT "localhost:9200/_cluster/settings" -H 'Content-Type: application/json' -d'
{
  "transient": {
    "cluster.routing.allocation.disk.watermark.low": "30mb",
    "cluster.routing.allocation.disk.watermark.high": "20mb",
    "cluster.routing.allocation.disk.watermark.flood_stage": "10mb",
    "cluster.info.update.interval": "1m"
  }
}
'

After doing that, you might need to unlock your cluster for write accesses if you had already exceeded your watermark before:

curl -XPUT -H "Content-Type: application/json" http://localhost:9200/_all/_settings -d '{"index.blocks.read_only_allow_delete": null}'

See How to fix ElasticSearch [FORBIDDEN/12/index read-only / allow delete (api)] for more details on that.

I do not recommend to set the values to zero (i.e. below 10 Megabytes) because using every byte of available disk space might cause issues on your system since more important applications will not be able to properly allocate disk space any more.

In order to view the current disk usage use

curl -XGET "http://localhost:9200/_cat/allocation?v&pretty"

See How to view & interpret disk space usage of your ElasticSearch cluster for more details.