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User profile for user: TBTFL
TBTFL Author
User level: Level 1
4 points

external drive available space calculation error?

Hi,


I recently noticed the 'available space' of an external drive doesn't make sense at all.


My external SSD is 512GB, and had about 250GB of free space a few days ago before I 'duplicated' a folder as big as 150GB.


I expected the external drive should have 100GB of free space, but it still says about 200GB is free. It didn't change after rebuilding spotlight index by using terminal command, mdutil -E / .


Looking into it, I checked the size of the biggest folder in the external SSD, and 'Get Info' windows says the folder is a little bigger than 400GB. However, still the macOS diskutility says my external drive has more than 200GB of free space.


Should I be worried about data loss or is it just an error of macOS(probably it will be updated after time-consuming spotlight index rebuil?)


Anything helps. Thanks!

Posted on Jul 3, 2022 4:23 PM

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User profile for user: HWTech
HWTech
User level: Level 9
60,380 points

Posted on Jul 3, 2022 4:58 PM

The APFS file system behaves differently than other older file systems. When you "copy" an item on an APFS file system, then the file system just creates a new link to the exact same data on the drive. Only when you modify the contents of one of those links do things change a bit. The APFS file system can be a bit confusing.


See these articles for some details on some of the changes and new features the APFS file system has (some are more detailed than others):

File system formats available in Disk Utility on Mac - Apple Support


https://www.backblaze.com/blog/apfs-apple-file-system/


https://eshop.macsales.com/blog/36808-tech-101-we-explain-the-new-apple-file-system-apfs/


https://arstechnica.com/gadgets/2016/06/digging-into-the-dev-documentation-for-apfs-apples-new-file-system/


https://en.wikipedia.org/wiki/Apple_File_System


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User profile for user: HWTech
HWTech
User level: Level 9
60,380 points

Jul 3, 2022 4:58 PM in response to TBTFL

The APFS file system behaves differently than other older file systems. When you "copy" an item on an APFS file system, then the file system just creates a new link to the exact same data on the drive. Only when you modify the contents of one of those links do things change a bit. The APFS file system can be a bit confusing.


See these articles for some details on some of the changes and new features the APFS file system has (some are more detailed than others):

File system formats available in Disk Utility on Mac - Apple Support


https://www.backblaze.com/blog/apfs-apple-file-system/


https://eshop.macsales.com/blog/36808-tech-101-we-explain-the-new-apple-file-system-apfs/


https://arstechnica.com/gadgets/2016/06/digging-into-the-dev-documentation-for-apfs-apples-new-file-system/


https://en.wikipedia.org/wiki/Apple_File_System


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external drive available space calculation error?

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