On Sat, Nov 26, 2011 at 8:39 PM, Michał Górny <mgo...@gentoo.org> wrote: > But in this particular case, I don't think COW is particularly useful. > If it works only on filesystem bounds, we could move the file directly > anyway. >
There are still a few specific cases in which CoW would indeed be useful. IIRC, reflinking of files works across btrfs *subvolumes*, and such a copy would normally be detected as a cross-device move. Another use would be an patch-merge which makes use of *ranged reflinks* to only CoW copy those parts of the file that were changed[1]. rsync has support for this, but only while appending to files (--append-verify --no-whole-file). 1. Somewhat like rope data structures, with the caveat that ranges must be block-size aligned. -- ~Nirbheek Chauhan Gentoo GNOME+Mozilla Team
