I use btrfs, and you can make a copy-on-write "copy", that's something like a hardlink until you modify one of the copies. That makes the copy less backup-like, but it is much faster. Vifm 0.7.8 does not seem to do it.
I wasn't aware of this feature of btrfs. It seems to be quite easy to implement for both 'syscalls' and 'nosyscalls' cases, so this should be in the next version and will require enabling some option (as it's set to never by default in cp).
FWIW, it also applies to mv, where reflink=auto may be the default recently (coreutils 8.24?): https://lists.gnu.org/archive/html/coreutils/2014-09/msg00002.html
I have a Bash alias defined, adding "reflink=auto" to cp. Maybe Vifm could detect that (even if optionally)?
Then maybe just use auto by default, this would make it simpler. Moving between mount boundaries is just copy+delete, so it will work automatically.
aliases are not exported by shells and parsing configuration of a shell is problematic, this can't be done properly by Vifm on its own.
In master now. I ended up adding an option 'iooptions', so one needs to set it to fastfilecloning, linked message raises valid concern about unexpected slowdown due to COW and I don't want fix the behaviour.