Mac storage basics · External storage and adding space

What's the safest way to copy a large folder to an external drive?

Short answer: Check space and format, copy with Finder without interruptions, compare item counts and sizes, open a few files, and only then delete the originals.

Copy first, check the copy, and only then delete anything.

  1. Make sure the drive has enough free space and a suitable format (APFS for Mac-only use).
  2. Copy with Finder, leaving the Mac awake and the drive connected until it finishes.
  3. Compare the item count and size of the copy with the original (Command-I on each).
  4. Open a few files from the copy.
  5. Only then delete the original, if that was the goal.

Interrupted copies can leave partial folders, so check before deleting anything. Storage Studio checks each move against the original before the original is touched, and leaves a link in its place.

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