I'm using a Lacie Biggest Quadra 4tb drive for a project. It was working fine for a couple of weeks and all of a sudden it has started acting weird. Files have started disapearing and sometimes it won't mount. I thought maybe it was that particular drive so I purchased a second one to backup to. Once the files were copied over the second drive started doing the same thing. Has anyone ever experienced this?
Has your machine been crashing/freezing forcing you to restart? If so, or even if not try running a utility such as Disk warrior, Drive Genius or Tech tool to check/repair the volume information.
Also I've noticed drives act goofy if they were not formatted for Mac OS before using (Im not sure if all Lacie drives are Mac formatted out of the box) so check to make sure the drive is formatted for Mac OS.
Make sure your drive isn't completely full - leaving around 5% free on your drive is a good thing.