You connect an external SSD or hard drive to your MacBook through a USB-C hub and start a Time Machine backup.
Everything appears normal, but macOS stays on:
“Preparing Backup…”
for a long time.
Before replacing your USB-C hub or external drive, it is important to understand what happens during this stage.
Time Machine does not immediately copy files when a backup starts. macOS first analyzes your files, compares previous backups, calculates changes, and prepares the backup structure.
However, if Time Machine remains stuck on “Preparing Backup” and never moves forward, the issue may come from:
- external drive format;
- storage performance;
- file indexing;
- USB-C connection stability;
- power or device compatibility.
This guide explains how to identify the cause and build a more reliable Mac backup setup.
Why Does Time Machine Stay on “Preparing Backup”?
Many users assume that “Preparing Backup” means the backup has already started transferring files.
Actually, this stage happens before most data copying begins.
During preparation, macOS may:
- scan files;
- identify changed data;
- compare previous backup versions;
- estimate backup size;
- create the backup process.
According to Apple's Time Machine backup requirements, Time Machine is designed to automatically back up your Mac and maintain previous versions of files for recovery.
For a first-time backup, this process can take much longer because macOS needs to analyze a large amount of data.
However, if the preparation stage never completes, your storage setup needs further checking.
Step 1: Check Your External Backup Drive First
Before troubleshooting the USB-C hub, verify that your external drive is ready for Time Machine.
Check the Drive Format
The file system plays an important role in Mac backups.
Modern macOS versions work best with APFS-formatted drives for Time Machine.
A drive may still appear normally in Finder while having a format that is not ideal for backup performance.
Before changing the format:
- Back up important files.
- Open Disk Utility.
- Check the current drive format.
- Reformat only if necessary.
Apple explains how to format an external drive for Mac backup using Disk Utility.
Check Available Storage Space
Time Machine needs enough free space to create and manage backup versions.
A nearly full external drive may cause:
- longer preparation times;
- repeated backup cleanup;
- failed backup attempts.
For regular backups, choose a drive with enough capacity for your current files and future growth.
Check Long-Term Storage Performance
External SSDs often advertise high peak speeds, but Time Machine depends more on consistent performance.
A drive may slow down during long operations because of:
- cache exhaustion;
- thermal throttling;
- internal storage management.
This means:
Peak speed ≠ sustained backup performance
A drive that is fast during a short file transfer may still struggle during hours of continuous backup activity.
If your external storage slows during large transfers, our guide about external SSD write speed drops during large file transfers explains why storage performance can change over time.
Step 2: Understand How USB-C Hubs Affect Time Machine Backups
A USB-C hub does not automatically cause Time Machine problems.
However, it adds more components between your Mac and backup drive.
The connection path becomes:
MacBook → USB-C Hub → External SSD/HDD
Compared with:
MacBook → External SSD/HDD
The hub introduces additional factors:
- shared USB bandwidth;
- power distribution;
- cable quality;
- multiple connected devices;
- connection stability.
A common situation is:
- Finder file transfer works normally.
- The external drive appears correctly.
- Time Machine backup becomes stuck or disconnects.
Why?
Because Time Machine creates a long-running workload.
A file transfer may finish in minutes.
A Time Machine backup may continue for hours.
Long-duration stability matters more than short-term performance.
Step 3: Diagnose the Problem Based on What Happens
Use the symptom to narrow down the cause.
| What Happens | Possible Cause |
|---|---|
| Preparing Backup stays for a very long time | File scanning, indexing, or drive format |
| Backup works directly but fails through the hub | USB-C connection path |
| External drive disconnects during backup | Cable, power, or hub stability |
| First backup takes many hours but completes | Normal behavior |
| Backup stops after connecting more devices | Shared bandwidth or power limitation |
Step 4: Run These Simple Backup Tests
Test 1: Connect the Drive Directly to Your Mac
Remove the USB-C hub temporarily.
Connect:
MacBook → External SSD/HDD
Then start Time Machine again.
If the backup works normally, investigate:
- USB-C hub compatibility;
- connected accessories;
- power distribution;
- connection stability.
Test 2: Disconnect Other USB Devices
Remove unnecessary devices:
- keyboards;
- webcams;
- card readers;
- additional storage devices.
Then test Time Machine again.
If the issue disappears, another connected device may be affecting the shared USB connection.
Test 3: Compare Different Backup Setups
Compare:
Portable Setup
MacBook → USB-C Hub → External Drive
Desktop Setup
MacBook → Docking Station → External Drive + Other Accessories
Users who keep a backup drive connected every day may benefit from a more stable desktop connection.
Build a Better Mac Time Machine Setup
A reliable backup workflow is not only about storage speed.
The entire connection chain matters:
Mac → USB-C Connection → Hub/Docking Station → External Drive
For Desktop MacBook Backup Workflows
For users who keep external drives connected at a workstation, a USB-C docking station with HDMI, Ethernet, and multiple USB ports, such as the LENTION D54, can simplify a permanent Mac setup.
It allows users to organize:
- external storage;
- displays;
- Ethernet;
- keyboards and mice;
- other daily accessories.
A docking station is a better fit for users who treat their MacBook as a desktop workstation.
For Simpler Backup Connections
For users who only need basic storage connectivity, a USB-C hub with HDMI and PD charging, such as the LENTION C35H, provides a compact way to connect external storage and everyday accessories.
This type of setup works well for:
- MacBook Air users;
- mobile offices;
- occasional backups;
- simple desk setups.
Improve Backup Reliability With These Tips
Before starting a long Time Machine backup:
Keep the Mac Connected to Power
Large backups can take significant time and battery.
Avoid Disconnecting Storage During Backup
Unexpected removal can interrupt the backup process and create additional issues.
Test Before Important Backups
Run a small backup test before relying on a new storage setup for important files.
FAQ
Why is Time Machine stuck on Preparing Backup?
Time Machine may remain on Preparing Backup while macOS scans files and prepares the backup database. If it never completes, check the drive format, storage space, indexing, and connection stability.
Can a USB-C hub affect Time Machine backups?
Yes. A USB-C hub can affect long-running backups if there are bandwidth limits, power issues, or unstable connections between the Mac and external drive.
How long should Time Machine stay on Preparing Backup?
The first backup can take much longer because macOS needs to analyze many files. If there is no progress for an unusually long time, check the storage setup and connection path.
Is SSD better than HDD for Time Machine?
An SSD usually provides faster access and better responsiveness, but a reliable backup setup also depends on capacity, format, and connection stability.
Final Thoughts
When Time Machine gets stuck on “Preparing Backup” through a USB-C hub, do not immediately replace the hub or external drive.
Start by checking:
- External drive format.
- Available storage space.
- Sustained storage performance.
- USB-C connection stability.
- Backup behavior with and without the hub.
A successful Time Machine backup depends on the entire setup working together.
Reliable backups require a stable connection path—not just a fast drive.
