LaCie unknown device is a common issue that people face when they connect the LaCie drive to Mac . LaCie external hard drive is quite popular and used by many peoples to extend the storage capacity of their Mac system. You must be storing important data in this reliable hard drive. But there can be certain unwanted situation when the hard drive become unresponsive or shows as LaCie unknown device on the Mac system. There can be many reasons for this you must first check the connection wire the drive if there is any fault then try to replace it and then reconnect. If you are still getting the same problem then there can be any file system error in the hard drive or malfunctioning of the components of the hard drive. File system errors can be fixed by formatting the hard drive but if the LaCie unknown device issue is caused by any physical defect you have send it for repairing . In both case the data lost in your LaCie hard drive will be lost and if you want to recover it you can use Mac data recovery software when it stops giving LaCie unknown device on your Mac.