External drives · Mounting and drive problems
What happens to my files if my Mac crashes or the drive unplugs during a copy?
Short answer: Your originals are safe: a copy leaves them untouched, and a Finder move between drives only removes the original after the copy finishes. Delete the partial copy, copy again, and run First Aid on the drive. Storage Studio keeps originals until its copy is checked.
With a normal copy, your originals are untouched; only the half-copied files at the destination may be incomplete. Delete the partial copy and copy again. A Finder move between drives also copies first and removes the original only once the copy finishes, so an interruption leaves the original in place.
Afterwards, run First Aid on the external drive if it was unplugged or lost power.
Storage Studio's own moves work the same safe way: the original stays where it is until the copy has been checked, and an interrupted move can be resumed or cleaned up — see what happens if you unplug without ejecting.