Re: cp command - problem with sparse

[James Youngman]

On Mon, Jan 31, 2005 at 05:30:22PM +0100, RE wrote:

> "cp --sparse=always c:\test.cfg c:\test2.cfg"
> 
> Everything works fine with that cp command, except the 
> fact that I do not get a sparse file.  Even when I copy 
> a sparse file, the sparse attribute is no longer 
> present in the copy an the occupied space on my HD is 
> the same as with the original file.
> 
> What am I doing wrong?
> 
> I tried already different PCs with NTFS (OS = Win2k 
> SP4)

Unix systems automatically generate sparse files when programs seek
forwards on their output file.  There is no need to have a "sparse"
attribute.  This is what coreutils' "cp" does.  

Windows and NTFS don't work in this way.  Under NTFS, there is, as you
say, a "sparse" attribute which must be set.  GNU coreutils runs on
Windows under Cygwin and am not sure if Cygwin exposes any form of API
which might allow cp to set the sparse attribute.  It's certainly a lot more 
complex to do this under Windows. 


See
http://www.ntfs.com/ntfs-sparse.htm
and
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/base/fsctl_set_zero_data.asp