Why back up before repair
Repairs that touch the SSD (board work, water damage, certain logic-board fixes) carry small risk of data loss. Apple-spec workshops always work to preserve data, but the only guarantee is a backup you control.
Even repairs that 'shouldn't' touch storage occasionally do — a slipped tool, a power glitch during testing, a corrupted file system encountered during diagnosis. Backup first, always.
What you need — external drive selection
Minimum: any USB-C or USB-A external SSD or HDD with capacity at least 2× your Mac's used storage. SSD is faster (recommended); HDD is cheaper.
In Pakistan, a 1TB Sandisk Extreme USB-C SSD costs PKR 12,000–15,000. A 2TB external HDD costs PKR 7,000–10,000. Either works. Avoid generic unbranded drives — they fail more often than they save.
Time Machine setup — 10 minutes
Plug the drive into the Mac. macOS will likely ask 'Do you want to use this drive with Time Machine?' Click 'Use as Backup Disk' and choose 'Encrypt Backup' (highly recommended — set a password you'll remember).
If macOS doesn't ask: System Settings → General → Time Machine → click + → choose the drive → Encrypt.
First backup takes 1–4 hours depending on data size. Leave the Mac plugged in. After it's done, you can disconnect the drive.
Alternative: iCloud + selective copies
If you don't have an external drive: enable iCloud Drive (System Settings → Apple ID → iCloud → iCloud Drive ON), set Desktop + Documents to sync, set Photos to upload. Your most-important files end up in iCloud.
Caveat: iCloud free tier is only 5GB. Paid (PKR 270/mo for 50GB, PKR 540/mo for 200GB) is needed for any real backup. Slower than Time Machine but doesn't need any hardware purchase.
Verify the backup actually worked
Time Machine: System Settings → General → Time Machine → check 'Latest Backup' shows a recent timestamp. Click 'Browse Time Machine' (or use the menu bar icon) and confirm you can see your files in the snapshot.
iCloud: open Files app on your iPhone, go to iCloud Drive folder, verify your Mac's Desktop and Documents folders appear with files inside.