Mac is used as for for professional use and any important data is saved in the Mac drive. If any extra storage is needed then Mac users rely on the Lacie external drive and it has better performance and data security. But what if the the Mac lacie drive not mounting then all the data will be inaccessible and you copy or write any file to the drive. The first possibility is that the drive is not connected well then you have to attach it properly and then mount it. If it is still not solving then the chances are that the drive is corrupted which can be caused if the drive was unexpectedly detached from the system, The file system of the drive has been damaged by some malicious files. You can check the drive by connection it to other system if Mac Lacie drive not mounting then you can use disk utility to format the lacie drive which will remove all the error and also erase the data. Now you can recover the data by using the lacie drive recovery software which can restore all the files back in the drive after the scanning. You can scan the drive after you fix Mac Lacie drive not mounting and you will get the preview of the files that you have lost.