6.0 marshmallow - Why does Android show more space used in internal storage than what adds up in the details?

I have a Moto G (3g) with Android 6. I noticed that When I go to Settings>Storage>Internal Storage, it shows that 2.85GB are being used out of 11.81GB. However, If I add up the storage shown for each category, the results are less than what is shown as total usage. This are the values shown:

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Apps: 1.25GB

Images: 10.74MB

Videos: 0.00 B

Audio: 0.00 B

Misc.:1.62MB

Cache: 6.97MB

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I have used several tools (like Storage Space) and they all show the same.

I used DiskUsage and it shows a "System data" used storage, that fills in the gap.

I know Android has a system partition, but this "System data" is shown in the data partition.

Why does this happen? What is stored in "System Data"?

Answer

DiskUsage is giving you the correct information. Per the developer of DiskUsage:

System data consists of several things:

1. 
   

   Unpacked dalvik bytecodes corresponding to your installed apks. If you install app on external storage, it still consumes space on your data partition.

   
   



2. 
   

   Crash dumps stored in tombstones directory.

   
   


3. 
   

   Any other data or settings android store on your device.

   
   

This data is hidden and DiskUsage can't easily identify how much space each of this consume. Usually (1) consumes most, so if you want to cleanup some space you may want to delete apps on external storage.

http://androidforums.com/threads/disk-usage.181747/