You can make a difference in the Apple Support Community!

When you sign up with your Apple Account, you can provide valuable feedback to other community members by upvoting helpful replies and User Tips.

Looks like no one’s replied in a while. To start the conversation again, simply ask a new question.

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

Reply
Question marked as Top-ranking reply
User profile for user: HWTech
HWTech
User level: Level 9
60,374 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


View in context

Similar questions

1 reply
Question marked as Top-ranking reply
User profile for user: HWTech
HWTech
User level: Level 9
60,374 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


Reply

external drive available space calculation error?

Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple Account.
Learn more Sign up