How to find out the real size of a file on disk?

Question

linux

How to find out the real size of a file that is on the file system and compressed (btrfs zlib) ?. du shows how much the file weighs in the end, when the FS uncompressed it and "give it away". du --apparent-size doesn't show this info..

Answer 1

No way.
https://btrfs.wiki.kernel.org/index.php/Compressio...
> There is a patch adding support fort that, currently it's not merged. You can kind of guess at its compressed size by comparing the output from the "df" command before and after writing a file, if this is available to you.