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Elastic Docs ›Elasticsearch Guide [8.16] ›Troubleshooting ›Fix common cluster issues

Fix watermark errors

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Fix watermark errors

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When a data node is critically low on disk space and has reached the flood-stage disk usage watermark, the following error is logged: Error: disk usage exceeded flood-stage watermark, index has read-only-allow-delete block.

To prevent a full disk, when a node reaches this watermark, Elasticsearch blocks writes to any index with a shard on the node. If the block affects related system indices, Kibana and other Elastic Stack features may become unavailable. For example, this could induce Kibana’s Kibana Server is not Ready yet error message.

Elasticsearch will automatically remove the write block when the affected node’s disk usage falls below the high disk watermark. To achieve this, Elasticsearch attempts to rebalance some of the affected node’s shards to other nodes in the same data tier.

Monitor rebalancing

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To verify that shards are moving off the affected node until it falls below high watermark., use the cat shards API and cat recovery API:

GET _cat/shards?v=true

GET _cat/recovery?v=true&active_only=true

If shards remain on the node keeping it about high watermark, use the cluster allocation explanation API to get an explanation for their allocation status.

GET _cluster/allocation/explain
{
  "index": "my-index",
  "shard": 0,
  "primary": false
}

Temporary Relief

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To immediately restore write operations, you can temporarily increase the disk watermarks and remove the write block.

PUT _cluster/settings
{
  "persistent": {
    "cluster.routing.allocation.disk.watermark.low": "90%",
    "cluster.routing.allocation.disk.watermark.low.max_headroom": "100GB",
    "cluster.routing.allocation.disk.watermark.high": "95%",
    "cluster.routing.allocation.disk.watermark.high.max_headroom": "20GB",
    "cluster.routing.allocation.disk.watermark.flood_stage": "97%",
    "cluster.routing.allocation.disk.watermark.flood_stage.max_headroom": "5GB",
    "cluster.routing.allocation.disk.watermark.flood_stage.frozen": "97%",
    "cluster.routing.allocation.disk.watermark.flood_stage.frozen.max_headroom": "5GB"
  }
}

PUT */_settings?expand_wildcards=all
{
  "index.blocks.read_only_allow_delete": null
}

When a long-term solution is in place, to reset or reconfigure the disk watermarks:

PUT _cluster/settings
{
  "persistent": {
    "cluster.routing.allocation.disk.watermark.low": null,
    "cluster.routing.allocation.disk.watermark.low.max_headroom": null,
    "cluster.routing.allocation.disk.watermark.high": null,
    "cluster.routing.allocation.disk.watermark.high.max_headroom": null,
    "cluster.routing.allocation.disk.watermark.flood_stage": null,
    "cluster.routing.allocation.disk.watermark.flood_stage.max_headroom": null,
    "cluster.routing.allocation.disk.watermark.flood_stage.frozen": null,
    "cluster.routing.allocation.disk.watermark.flood_stage.frozen.max_headroom": null
  }
}

Resolve

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As a long-term solution, we recommend you do one of the following best suited to your use case:

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