# High Disk Read I/O in Elasticsearch

**URL:** <https://discuss.elastic.co/t/high-disk-read-i-o-in-elasticsearch/104232>\
**Category:** Elasticsearch\
**Created:** [October 17, 2017, 11:21am UTC](https://discuss.elastic.co/t/high-disk-read-i-o-in-elasticsearch/104232 "2017-10-17T11:21:20Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Deb](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/deb/32/46162_2.png) [@Deb](https://discuss.elastic.co/u/Deb)\
**Post date:** [October 17, 2017, 11:21am UTC](https://discuss.elastic.co/t/high-disk-read-i-o-in-elasticsearch/104232/1 "2017-10-17T11:21:20Z")

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I am observing a high disk read i/o in a elasticsearch node. I am using one node cluster with 5 shards.

**Environment**

1. Elasticssearch 2.3.1
2. Disk SSD
3. Cores - 16
4. RAM - 64 GB

Segments and merging could be one of the issue. But as mentioned in this [link](https://www.elastic.co/guide/en/elasticsearch/guide/current/indexing-performance.html#segments-and-merging) I don't see any INFO log stating `now throttling indexing`.

Can someone let me know what could be the problem and how can I debug this issue?

The node stats looks like below:-1:

[https://gist.github.com/debraj-manna/296956d1456ac8094a6c532b238537cb](https://gist.github.com/debraj-manna/296956d1456ac8094a6c532b238537cb)

`index.refresh_interva`l and `index.translog.flush_threshold_size` are both set to default values.

hot-threads report is as follows:- (\_nodes/hot\_threads?pretty") -

```
Hot threads at 2017-10-17T12:45:39.517Z, interval=500ms, busiestThreads=3, ignoreIdleThreads=true:

   71.6% (357.8ms out of 500ms) cpu usage by thread 'elasticsearch[Axum][[denorm][1]: Lucene Merge Thread #6011]'
     3/10 snapshots sharing following 13 elements
       org.apache.lucene.index.MultiTermsEnum.pushTop(MultiTermsEnum.java:275)
       org.apache.lucene.index.MultiTermsEnum.next(MultiTermsEnum.java:301)
       org.apache.lucene.index.FilterLeafReader$FilterTermsEnum.next(FilterLeafReader.java:195)
       org.apache.lucene.codecs.blocktree.BlockTreeTermsWriter.write(BlockTreeTermsWriter.java:438)
       org.apache.lucene.codecs.perfield.PerFieldPostingsFormat$FieldsWriter.write(PerFieldPostingsFormat.java:198)
       org.apache.lucene.codecs.FieldsConsumer.merge(FieldsConsumer.java:105)
       org.apache.lucene.index.SegmentMerger.mergeTerms(SegmentMerger.java:193)
       org.apache.lucene.index.SegmentMerger.merge(SegmentMerger.java:95)
       org.apache.lucene.index.IndexWriter.mergeMiddle(IndexWriter.java:4075)
       org.apache.lucene.index.IndexWriter.merge(IndexWriter.java:3655)
       org.apache.lucene.index.ConcurrentMergeScheduler.doMerge(ConcurrentMergeScheduler.java:588)
       org.elasticsearch.index.engine.ElasticsearchConcurrentMergeScheduler.doMerge(ElasticsearchConcurrentMergeScheduler.java:94)
       org.apache.lucene.index.ConcurrentMergeScheduler$MergeThread.run(ConcurrentMergeScheduler.java:626)
```

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [November 14, 2017, 11:21am UTC](https://discuss.elastic.co/t/high-disk-read-i-o-in-elasticsearch/104232/2 "2017-11-14T11:21:23Z")

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