BTRFS File-level cloning in a split of a second.

Clone a file on btrfs in a split of a second

cp --reflink=always file.img clone_of_file.img

Before copying file
$ ls -s1
10485760 Centos53-2.img

Copying 10GB file
$ time cp --reflink=always  Centos53-2.img Centos53-2_copy.img

real    0m0.001s
user    0m0.000s
sys     0m0.000s

After copying file 
$ ls -s1
10485760 Centos53-2_copy.img
10485760 Centos53-2.img