I bought a new hdd for my file server, copied all over to the new disk, and gave it the same drive letter and name, so the change would be transparent to all machines connected to the network. Once done, the old partition has been unmounted/unmapped (no more drive letter, so - I thought - no more possibility of access).
It almost worked. All machines have access to the new folders, but for those that were already connected to the AD, new files or new versions have been written in the old disk, even after it was unmounted. It seems everything's working fine now, after all machines have restarted, but I cannot find an explanation for it (I can imagine, but nothing concrete popped up on my searches).