Elasticsearch Disk Watermark

Elasticsearch Disk Watermark

Opster Team

March 2021

In addition to reading this guide, we recommend you run the Elasticsearch Health Check-Up. It will detect issues and improve your Elasticsearch performance by analyzing your shard sizes, threadpools, memory, snapshots, disk watermarks and more.

The Elasticsearch Check-Up is free and requires no installation.

Run the Elasticsearch check-up to receive recommendations like this:

checklist Run Check-Up

The following configuration error was detected on node 123...



This error can have a severe impact on your system. It's important to understand that it was caused by...



In order to resolve this issue and prevent it from occurring again, we recommend that you begin by changing the configuration to...


X-PUT curl -H "Content-Type: application/json" [customized recommendation]


There are various “watermark” thresholds on your Elasticsearch cluster. As the disk fills up on a node, the first threshold to be crossed will be the “low disk watermark”. The second threshold will then be the “high disk watermark threshold”. Finally, the “disk flood stage” will be reached. Once this threshold is passed, the cluster will then block writing to ALL indices that have one shard (primary or replica) on the node which has passed the watermark. Reads (searches) will still be possible.

Relevant settings

cluster.routing.allocation.disk.watermark have three thresholds of watermarks, it accepts absolute values as well as percentage values. The three watermarks are:

  1. Low disk watermark
  2. High disk watermark
  3. Flood stage disk watermark

How to fix log messages related to disk watermarks

Permanent fixes

1. Delete unused indices

2. Merge segments to reduce the size of the shard on the affected node

3. Attach external disk or increase the disk used by the data node

Temporary hacks/fixes

1. Changed these settings values to a higher threshold by dynamically update settings using below update cluster API.

PUT _cluster/settings :


  “transient”: {

    “cluster.routing.allocation.disk.watermark.low”: “100gb”, –>adjust according to your situations

    “cluster.routing.allocation.disk.watermark.high”: “50gb”,

    “cluster.routing.allocation.disk.watermark.flood_stage”: “10gb”,

    “cluster.info.update.interval”: “1m”



2. Disable disk check by hitting below cluster update API


    “transient”: {

       “cluster.routing.allocation.disk.threshold_enabled” : false



Even After all these fixes, Elasticsearch won’t bring indices in write mode for that this API needs to be activated

PUT _all/_settings


     “index.blocks.read_only_allow_delete”: null


Run the Check-Up to get a customized report like this:

Analyze your cluster