Cleaning up an old external drive on Mac
Years of backups onto the same external drive leave it cluttered with duplicates. Here's a safe way to reclaim space.
That 1 TB external drive you bought in 2017 has been “the backup drive” through three Macs and probably four cleanups that weren’t really cleanups. It’s got Backup, Backup_old, iPhoto Library_2019, and a folder called Stuff that’s 80 GB of you-don’t-remember-what.
A reasonable plan
Don’t try to organize the drive. Just remove the duplicates, see what’s left, then decide what to keep.
Step 1: Check the drive’s health first
- Open Disk Utility.
- Select the external drive in the sidebar.
- Click “First Aid” and run it. If it reports errors, copy what you care about off the drive before doing anything else.
- Note the free space before cleanup so you can compare after.
Step 2: Run a dedupe scan
- Download Dupe and open it.
- Click “Add Folder” and select the external drive.
- Click “Scan.” External drives are slower than internal SSDs, so a large drive may take an hour or more for the full SHA-256 pass.
- Browse the duplicate groups. Each group shows full paths, so you can see whether two copies live in
BackupandBackup_oldor somewhere weirder. - Move copies to the Trash. Dupe uses the drive’s own
.Trashesfolder so deleted files remain recoverable on the drive itself.
Step 3: Empty the Trash from the drive
Empty the Mac’s Trash to actually reclaim the space. If the drive is formatted FAT32 or exFAT, files don’t move to a recoverable Trash and Dupe will warn you before deleting.
What you’ll likely find
- Three or four copies of your old Pictures folder from different Macs.
- An iTunes Music folder duplicating songs that are also in your current Music library.
- Multiple full Desktop folders from past computers.
- Old Time Machine backups (these are tricky — see below).
What to skip
- Old Time Machine sparse bundles or
.backupbundlefiles. Don’t dedupe inside Time Machine backup structures. Dupe leaves these alone. - Disk images (
.dmg,.sparseimage). Dupe will hash these like any other file, which is fine. But don’t delete a disk image just because there’s another file inside it that’s a duplicate. - System folders and hidden directories — excluded automatically.
Safety
- Trash-only deletion. The drive’s
.Trashesfolder holds files for recovery. - Byte-identical matching only.
- macOS metadata folders like
.fseventsdand.Spotlight-V100are skipped.
Old external drives often free 200–500 GB on a single pass.
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