free_disk_space 
Simple class that shows free disk space for directory. Return free disk space as float.
Usage
gem install free_disk_space
OR in Gemfile:
gem 'free_disk_space'
Then just use in code:
FreeDiskSpace.terabytes('/')
FreeDiskSpace.gigabytes('/')
FreeDiskSpace.megabytes('/')
FreeDiskSpace.kilobytes('/')
FreeDiskSpace.bytes('/')
OR:
free_disk_space = FreeDiskSpace.new('/')
free_disk_space.terabytes
free_disk_space.gigabytes
free_disk_space.megabytes
free_disk_space.kilobytes
free_disk_space.terabytes