An external drive is the fastest destination you can give macup. Thunderbolt writes at local-disk speeds, restores take minutes instead of hours, and the per-terabyte cost is the lowest of any destination you can pick. It is also the most fragile destination you can pick — a drive in the same building as your Mac shares every failure the Mac has.
Use external drives. Do not rely on them alone.
When an external drive is the right call
- First seed. Seeding 4 TB to a local drive over Thunderbolt takes an hour; seeding it to any cloud takes days.
- Large restores. A ransomware event where you need every byte back by Monday — a local drive gets you there.
- Travel. A bus-powered drive in your bag is an offline copy of your work that no network outage can reach.
- Per-terabyte cost. Under $20 per terabyte for spinning disk, under $80 for SSD. Nothing else comes close.
The full comparison lives in /backup/guides/cloud-vs-local-backup.
When an external drive is not enough
External drives share a failure domain with your Mac. The list of things that destroy both at once is long:
- A house fire.
- A flood or a burst pipe.
- A single ransomware event — if the drive is mounted, the malware gets to it too.
- A theft where the bag and the laptop leave together.
- A power surge.
Pair an external drive with a cloud destination. Do not replace one.
Step 1 — Plug in the drive
macOS mounts USB, USB-C, and Thunderbolt drives automatically. You should see the drive in Finder within a few seconds.
Step 2 — Format the drive (optional but recommended)
If the drive is new or you are dedicating it to macup, reformat it first:
Reformat in Disk Utility
- Open Disk Utility.
- Select the drive on the left — the top-level device, not a partition.
- Click Erase.
- Name: macup-backup-1 (or similar).
- Format: APFS.
- Scheme: GUID Partition Map.
- Click Erase.
Reformatting destroys everything on the drive. Only do this on a drive you are dedicating to macup backups.
Step 3 — Add the destination in macup
Open macup > Preferences > Destinations. Click Add destination. Choose External drive.
Step 4 — Pick the drive
macup lists every currently-mounted drive that is writable. Pick the one you just plugged in and formatted. macup creates its repository at /Volumes/<drive-name>/macup-repository/.
Step 5 — Point a backup set at it
Go to Backup Sets, pick your set, open Destination, and select the drive. The flow is identical to picking macup Cloud or a BYOS bucket — a destination is a destination.
Step 6 — The “only when mounted” flag
In the destination settings, toggle Only back up when mounted if this is a drive you do not keep permanently connected — a travel drive, a dock-tethered drive, a drive you rotate offsite.
With this flag on, macup:
- Skips the destination silently when the drive is unplugged — no red error, no alert, no daemon retry storm.
- Resumes automatically the next time the drive appears.
- Shows a “last seen” timestamp so you know when it last got a snapshot.
Without this flag, an unplugged drive surfaces as a failing destination in the status bar. That is correct for a drive you expect to always be connected, and wrong for a drive you travel with.
Safety tips
- Rotate two drives. Drive A lives at home. Drive B lives at a friend’s house, a parent’s house, or a safe-deposit box. Swap them monthly. Now a house fire is not the end of your archive.
- Use Object Lock where the filesystem supports it. On Synology, TrueNAS, and most NAS targets, you can turn on object-level immutability. Do it. That is your local ransomware defence.
- Buy the right drive, not the cheapest drive. Year-five failure rates on the cheapest consumer drives are significantly worse than name-brand enterprise drives. The numbers, with sources, are on /backup/drive-failure.
- Test a restore every quarter. Plug the drive in, pick a folder you did not intentionally change, and restore it to a scratch location. A backup you have never restored from is a rumour.
External drives are the fastest, cheapest, most fragile destination you have. Treat them as one leg of the stool, not the whole stool.