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====== SnapRAID - Scrub for Bit Rot ======

Over time, files can become corrupted due to bit rot.

  * SnapRAID can scrub files to detect and correct errors.

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===== Scrub =====

<code bash>
sudo snapraid scrub
</code>


<WRAP info>
**NOTE:**  This command verifies the data in your array comparing it with the hash computed in the "sync" command.

  * Every run of the command checks about the 8% of the array, but not data already scrubbed in the previous 10 days.

</WRAP>

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===== Scrub using different options =====

The **-p**, **--plan** option can be used to specify a different amount, and the **-o**, **--older-than** option to specify a different age in days.

For example, to check 5% of the array older than 20 days use: 
<code bash>
sudo snapraid scrub -p 10
</code>

<WRAP info>
**NOTE:**  Scrubbing should be run periodically to catch issues before they become serious.

  * **-p 10**: limits scrubbing to 10% of files, reducing disk wear.

</WRAP>

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===== Errors found during a scrub =====

If during the scrub process, silent or input/output errors are found, the corresponding blocks are marked as bad in the "content" file, and listed in the "status" command.

<code bash>
snapraid status
</code>


To fix them, you can use the **"fix"** command filtering for bad blocks with the **-e**, **--filter-error** options:
	
<code bash>
snapraid -e fix
</code>

<WRAP info>
**NOTE:**  At the next "scrub" the errors will disappear from the "status" report if really fixed.

  * To make it fast, you can use **-p bad** to scrub only blocks marked as bad: <code bash>
snapraid -p bad scrub</code>

</WRAP>

<WRAP warning>
**WARNING:**  Take care that running "scrub" on a not synced array may result in errors caused by removed or modified files.

  * These errors are reported in the "scrub" result, but related blocks are not marked as bad. 
</WRAP>

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