# Behavior of ForceMerge **URL:** \ **Category:** Elasticsearch\ **Created:** [June 25, 2019, 2:59am UTC](https://discuss.elastic.co/t/behavior-of-forcemerge/187219 "2019-06-25T02:59:52Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Taaaak](https://avatars.discourse-cdn.com/v4/letter/t/8491ac/32.png) [@Taaaak](https://discuss.elastic.co/u/Taaaak)\ **Post date:** [June 25, 2019, 2:59am UTC](https://discuss.elastic.co/t/behavior-of-forcemerge/187219/1 "2019-06-25T02:59:53Z")
Let me ask about the behavior of \_forcemerge API including parameter `only_expunge_deletes=true`. I'm planning to execute `_forcemerge?only_expunge_deletes=true` to large index (more over 500GB/10 datanodes) to clean up a disk space. So my question is, does it API use additional disk space to clean deleted documents, if yes how large does it consume? ---
**Author:** ![Christian\_Dahlqvist](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/christian_dahlqvist/32/4617_2.png) [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)\ **Post date:** [June 25, 2019, 5:56am UTC](https://discuss.elastic.co/t/behavior-of-forcemerge/187219/2 "2019-06-25T05:56:18Z")
As all segments in Lucene are immutable new segments without the deleted documents will be created before the old ones are deleted. A forcemerge can therefore use a fair bit of additional disk space while it is running. I do not know how to predict exactly how much it needs as this depends on the parameters used and how the current segment distribution looks like. ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [July 23, 2019, 5:56am UTC](https://discuss.elastic.co/t/behavior-of-forcemerge/187219/3 "2019-07-23T05:56:27Z")
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