On 2017-08-03 13:15, Marat Khalili wrote:
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?)
OK, I think there may be some misunderstanding here. By 'CoW unwritten
extents', I mean that when we write to the extent, a CoW operation
happens, instead of the data being written directly into the extent. In
this case, it has nothing to do with reflinking, and Goffredo is correct
that if your filesystem is small enough, the second fallocate will fail
there.
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