On Fri, Oct 16, 2015 at 08:50:41AM -0400, Austin S Hemmelgarn wrote:

Certain parts of userspace do try to reflink things instead of copying (for
example, coreutils recently started doing so in mv and has had the option to
do so with cp for a while now), but a properly designed general purpose
filesystem does not and should not do this without the user telling it to do
so.

But they do.  Get out of your narrow local Linux file system view.
Every all flash array or hyperconverge hypervisor will dedeup the hell
out of your data, heck some SSDs even do it on the device.  Your NFS or
CIFS server already does or soon will do dedup and reflinks behind the
scenes, that's the whole point of adding these features to the protocol.

And except for the odd fear or COW or dedup, and the ENOSPC issue for
which we have a flag with a very well defined meaning I've still not
heard any good arguments against it.