> Yes, try it with dd and cp (GNU version only?): > > dd if=/dev/zero of=/tmp/zero-test count=1000 > cp --sparse=always /tmp/zero-test /tmp/zero-sparse > ls -l /tmp/zero-test /tmp/zero-sparse > du -cs /tmp/zero-test /tmp/zero-sparse > [...] > What I do not know is how many fs support it, and if they can do on > the fly or a forced copy is needed It is the copy which makes the sparse file. You can't make a hole in a file merely by writing a bunch of zeros to it. You can only do it by seeking past the (current) end of the file, then writing non-zero data. The bytes you seeked over are the hole, and will be read as if zeros. GNU cp uses a bunch of heuristics to discover runs of zeros in the input file and seek over them in the output file, rather than just writing zeros. Austin
