You are in a big trouble because the Lacie drive not readable on Mac. You were using the lacie external drive because the Mac storage is limited and it is easy to trasfer the data through it. There are many important and large files stored in the Lacie drive but now they have become inaccessible because of the problem in the Lacie drive. When you connect the drive to your Mac system to copy or move any data you are are getting the problem Lacie drive not readable on Mac. This can happen if the connector of the drive is damaged so you can try to change it. If the drive is still not readable then the corruption of lacie drive has taken place. You may have disconnected it from the sytem when the data transfer was going on, any partitioning error or may be it is infected with any malware program. In such situation you have to format the drive and then you can restore the data with the help of any backup. If the backup is not available then use the Lacie drive recovery software. It can run a thorough scan of the drive and then give you the preview of the files it found to choose and resstore. You should download the software and get back your lost file from lacie drive.