# caseSensitiveFS=false (the default) scan performance penalty scales up, and it can be extreme

**URL:** https://forum.syncthing.net/t/casesensitivefs-false-the-default-scan-performance-penalty-scales-up-and-it-can-be-extreme/21969
**Category:** Feature
**Created:** [April 18, 2024, 2:05pm UTC](https://forum.syncthing.net/t/casesensitivefs-false-the-default-scan-performance-penalty-scales-up-and-it-can-be-extreme/21969 "2024-04-18T14:05:02Z")
**Posts on this page:** 1
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### Author: ![bt90](https://forum.syncthing.net/user_avatar/forum.syncthing.net/bt90/32/18565_2.png) [@bt90](https://forum.syncthing.net/u/bt90)
#### Post date: [April 19, 2024, 2:40pm UTC](https://forum.syncthing.net/t/casesensitivefs-false-the-default-scan-performance-penalty-scales-up-and-it-can-be-extreme/21969/14 "2024-04-19T14:40:07Z")

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> [@380k files, 24GB in directory results in very slow sync = 8 days](https://forum.syncthing.net/t/380k-files-24gb-in-directory-results-in-very-slow-sync-8-days/21488/26):
>
> so, here are some results && initial conclusions, probably some of you can add more. this machine was CPU constrained during Scanning&Synching, because of (random order): slow caseinsesitive comparison calls long filenames of 380k files slow cpu only one core used multiple os.reaadir calls during Scanning enabling caseSensitiveFS (which is not default in syncthing), reduced Scanning time from 105 minutes to 3 minutes, and Syncing was more/less very fast. after it, syncthing is still cp…

While readdir is quite costly, we’re using a lot of CPU time for the unicode stuff.

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