# IO spike: how to know if cluster rebalanced

**URL:** <https://discuss.elastic.co/t/io-spike-how-to-know-if-cluster-rebalanced/3521>\
**Category:** Elasticsearch\
**Created:** [November 4, 2010, 8:12pm UTC](https://discuss.elastic.co/t/io-spike-how-to-know-if-cluster-rebalanced/3521 "2010-11-04T20:12:11Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![John\_Chang](https://avatars.discourse-cdn.com/v4/letter/j/ecc23a/32.png) [@John\_Chang](https://discuss.elastic.co/u/John_Chang)\
**Post date:** [November 4, 2010, 8:12pm UTC](https://discuss.elastic.co/t/io-spike-how-to-know-if-cluster-rebalanced/3521/1 "2010-11-04T20:12:11Z")

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We saw a ~45 minute IO spike in our elastic search nodes today, and during that time, we had no spike in indexing or querying. The only thing we can guess happened was a rebalance. Is there any way we can confirm this theory for sure? What else might cause this spike if our idexing/querying nodes were spiking?

Thanks

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**Author:** ![kimchy](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/kimchy/32/44952_2.png) [@kimchy](https://discuss.elastic.co/u/kimchy)\
**Post date:** [November 4, 2010, 9:12pm UTC](https://discuss.elastic.co/t/io-spike-how-to-know-if-cluster-rebalanced/3521/2 "2010-11-04T21:12:05Z")

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One other reason for a spike in IO is large merge that happened to a lucene  
index. Each lucen index is constructed of several segments, which gets  
merged every so ofter (I can provide more details on how this works if  
needed). A spike might be caused because a large merge between big segments  
has occurred.

-shay.banon

On Thu, Nov 4, 2010 at 10:12 PM, John Chang [jchangkihtest2@gmail.com](mailto:jchangkihtest2@gmail.com)wrote:

> We saw a ~45 minute IO spike in our Elasticsearch nodes today, and during  
> that time, we had no spike in indexing or querying. The only thing we can  
> guess happened was a rebalance. Is there any way we can confirm this  
> theory  
> for sure? What else might cause this spike if our idexing/querying nodes  
> were spiking?
> 
> ## Thanks
> 
> View this message in context:  
> [http://elasticsearch-users.115913.n3.nabble.com/IO-spike-how-to-know-if-cluster-rebalanced-tp1844345p1844345.html](http://elasticsearch-users.115913.n3.nabble.com/IO-spike-how-to-know-if-cluster-rebalanced-tp1844345p1844345.html)  
> Sent from the Elasticsearch Users mailing list archive at [Nabble.com](http://Nabble.com).

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [July 6, 2017, 4:17am UTC](https://discuss.elastic.co/t/io-spike-how-to-know-if-cluster-rebalanced/3521/3 "2017-07-06T04:17:08Z")

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Closed on July 6, 2017, 4:17am UTC