# Does a rescan actually rehash everything?
**URL:** https://forum.syncthing.net/t/does-a-rescan-actually-rehash-everything/20978
**Category:** Support
**Created:** [October 23, 2023, 8:35pm UTC](https://forum.syncthing.net/t/does-a-rescan-actually-rehash-everything/20978 "2023-10-23T20:35:50Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@redsector72](https://forum.syncthing.net/u/redsector72)
#### Post date: [October 23, 2023, 8:35pm UTC](https://forum.syncthing.net/t/does-a-rescan-actually-rehash-everything/20978/1 "2023-10-23T20:35:50Z")
I may need some clarification. According to the docs I have understood that a rescan will rehash only files that have a modification in their time, size or permission bits. So if I restart syncthing, why does it takes so long to do a rescan? Is there something in the configuration that I should check?
As side note I have a 8TB drive splitted in 2/3 TB folders.
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### Author:  [@tomasz86](https://forum.syncthing.net/u/tomasz86)
#### Post date: [October 24, 2023, 3:38am UTC](https://forum.syncthing.net/t/does-a-rescan-actually-rehash-everything/20978/2 "2023-10-24T03:38:11Z")
Please read up [https://docs.syncthing.net/users/syncing.html#scanning](https://docs.syncthing.net/users/syncing.html#scanning). In short, it does not rehash anything. The only way to force a rehash of everything would to be reset the database.
Scanning can take a lot of time depending on many factors. You’ve only mentioned the size, however what’s more important is the type of storage (HDD vs SDD vs network, etc.) and the number of files. Scanning through millions of tiny files is going to be much slower than just a few large ones. Also, in the case of Windows, the antivirus software may affect scanning time quite heavily.
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### Author:  [@system](https://forum.syncthing.net/u/system)
#### Post date: [November 23, 2023, 3:38am UTC](https://forum.syncthing.net/t/does-a-rescan-actually-rehash-everything/20978/3 "2023-11-23T03:38:43Z")
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