# How bloom filters work

**URL:** <https://forum.storj.io/t/how-bloom-filters-work/12104>\
**Category:** FAQ\
**Created:** [March 2, 2021, 8:19am UTC](https://forum.storj.io/t/how-bloom-filters-work/12104 "2021-03-02T08:19:50Z")\
**Posts on this page:** 1\
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**Author:** ![BrightSilence](https://storj.bcdn.literatehosting.com/user_avatar/forum.storj.io/brightsilence/32/6048_2.png) [@BrightSilence](https://forum.storj.io/u/BrightSilence)\
**Post date:** [March 2, 2021, 8:29am UTC](https://forum.storj.io/t/how-bloom-filters-work/12104/2 "2021-03-02T08:29:25Z")

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The bloom filter is created to always match all pieces that should be on the node. The node then checks which pieces don’t match the bloom filter and removes them. (though for reasons of efficiency, the size of the bloom filter is reduced by making it match about 10% of what’s not supposed to be on the node as well. So with every run about 10% of garbage stays behind to be cleaned up the next time)

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