Error when backing device does not exist

[jeremyeder]

# rpm -q docker
docker-1.7.1-109.el7.x86_64

# grep ^DEVS /etc/sysconfig/docker-storage-setup
DEVS=/dev/vdx

# ./docker-storage-setup.sh 
./docker-storage-setup.sh: line 381: * 2 - 2048 : syntax error: operand expected (error token is "* 2 - 2048 ")
  Volume group "docker" not found
  Cannot process volume group docker
  Volume group "docker" not found
  Cannot process volume group docker