No Mountable File Systems & related Error messages However loss of the same can be troublesome as it very often fails with no mountable file systems error.ģ. It contains bit-by-bit image of data created with DD command. It is similar to that of drive volumes and the file is opened in finder in the way similar to that used by most of the drive volumes.The included feature of password protection and compression makes the file most reliable for distribution over network with security. DMG or disk mounted graphics files of mac OS X contains data and files so as to keep it safe, minimizing the chances of data loss from Mac system hard drives.