Internal file system error is a common error for Mac users caused due to any type of inconsistencies in HFS or HFS+ file system. Operating System malfunctioning, severe virus attack, hard drive crash, human error, abrupt system shutdown, hardware or software issue are some of the most reasonable factors which can cause emergence of internal file system error on Mac. However fortunately most of the time this can fixed easily with the help of Disk Utility or FSCK command. But in case if the problem is complicated and can not be fixed using these inbuilt features, then in such situation you can reformat your entire Mac system in order to fix this issue. While formatting your hard drive all your files will get removed from your system but it will also fix internal file system error on Mac. However after formatting the hard drive all the your files does not get wiped permanently from your system thus your can recover then easily. Backup can used to restore lost or formatted files on Mac if you have created. But if not then you can try Mac Data Recovery Software in order to rescue files from formatted mac system when internal file system error on Mac get fixed completely.