On August 3, 2017 7:01:06 PM GMT+03:00, Goffredo Baroncelli 
>The file is physically extended
>
>ghigo@venice:/tmp$ fallocate -l 1000 foo.txt

For clarity let's replace the fallocate above with:
$ head -c 1000 </dev/urandom >foo.txt

>ghigo@venice:/tmp$ ls -l foo.txt
>-rw-r--r-- 1 ghigo ghigo 1000 Aug  3 18:00 foo.txt
>ghigo@venice:/tmp$ fallocate -o 500 -l 1000 foo.txt
>ghigo@venice:/tmp$ ls -l foo.txt
>-rw-r--r-- 1 ghigo ghigo 1500 Aug  3 18:00 foo.txt
>ghigo@venice:/tmp$

According to explanation by Austin the foo.txt at this point somehow occupies 
2000 bytes of space because I can reflink it and then write another 1000 bytes 
of data into it without losing 1000 bytes I already have or getting out of 
drive space. (Or is it only true while there are open file handles?)
-- 

With Best Regards,
Marat Khalili
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