Many of the Mac user have faced the problem hfs+ unreadable catalog file. The catalog file of one or more disk volume becomes corrupted and the it will get inaccessible. You will not be able to read or write any data in that partition which finally results in data loss. The hfs+ unreadable catalog file problem occurs when there is any partition error, virus infection, system error or abrupt shut down while writing the data. This can be fixed by using the Disk utility that is built in the Mac. It can deal with the minor corruption issue of the catalog file and make it accessible but sometimes the it fails. In such case you have to format the disk as in result all the data will be lost but hfs+ unreadable catalog file will be fixed. You can recover the data if you have the backup of the lost data. You can also try to use the Time machine facility but if it is not available you can use Mac data recovery software. It will scan the formatted drive and then give you the preview of the files it found for recovery. You can select the files you want and the it will be restored back in the drive. You can now easily fix hfs+ unreadable catalog file issue and recover the data.