Congratulations on a great job thirtySeven.

Your documentation should specify the intended user. If that is another perl script, you also need a 'synopsis' which shows how you expect this file to be used.

A search of cpan finds a module Filesys::Btrfs. You may be able to use it to avoid the use of system.

Do you plan on implementing your 'btrfs snapshot manager' in perl? If so, convention suggests that you implement the components as modules (perlmod) rather than programs.