Last night I was not as awake as I thougt i was and I ended up formatting the wrong drive using GParted.....
I thought of testdisk to recover the lost partition but I don't really understand how to use it.
If I select an Intel partition type and then analyse --> deeper search it showing in the first second of the scan the correct (backup superblock ?) of my "Lacie1To" partition witch used to be the only Ext4 partition occupying all the disk.
But if I clicked on stop it doesn't show me the partition in the list.
So my question, what should I do with this info ?