Time Machine usually cannot find a backup disk because the drive is disconnected, not mounted, incorrectly formatted, unavailable over the network, or experiencing a permissions or hardware problem. Start by checking the cable, power, and Finder. Then verify that the disk appears in Disk Utility and select it again in System Settings.
Quick Answer
- Reconnect the backup drive directly to your Mac and make sure it has power.
- Open Finder and check whether the disk appears under Locations.
- Open Disk Utility, choose View > Show All Devices, and see whether the drive is detected.
- In System Settings, open General > Time Machine and add or select the disk.
- If the drive appears but cannot be used, run First Aid in Disk Utility.
- Do not erase the disk unless you are certain it contains no backups you need.
If the disk is missing from both Finder and Disk Utility, test another cable, port, or Mac before assuming the problem is caused by Time Machine.
Check the Simple Causes First
Before changing settings, rule out connection and power problems. These checks are quick and do not affect your backups.
Reconnect the drive
- Disconnect the backup disk from your Mac.
- If it has a separate power adapter, unplug and reconnect the adapter.
- Wait a few seconds, then connect the disk directly to the Mac.
- Avoid a USB hub, dock, monitor, or adapter temporarily if possible.
- If the drive has a power switch, turn it on.
Some portable hard drives draw power from the Mac. If the Mac or hub cannot supply enough power, the disk may repeatedly disconnect or never appear.
If your Mac uses USB-C or Thunderbolt and the drive uses another connector, try another compatible adapter or cable. A cable can provide power but still fail to carry data reliably.
Check Finder
The disk may be connected but hidden from Finder.
- Open Finder.
- Choose Finder > Settings from the menu bar.
- Select the General tab and enable External disks under “Show these items on the desktop.”
- Select the Sidebar tab and enable External disks under “Locations.”
Look under Locations in the Finder sidebar. If the disk appears, click its eject icon if one is shown, wait for it to disappear, and reconnect it. This safely refreshes the connection.
Do not unplug a disk while a backup is running. If Time Machine is active, wait for it to finish or stop the backup from the Time Machine menu before disconnecting the drive.
Restart the Mac
A restart can clear a temporary connection or storage-service problem.
- Save your work.
- Close open apps.
- Choose Apple menu > Restart.
- Reconnect the backup disk after macOS starts.
If the disk works after restarting but disappears again later, suspect a failing cable, unstable hub, insufficient power, or a disk beginning to fail.
Check Whether macOS Detects the Disk
Disk Utility can detect a physical drive even when Finder cannot open its volume.
- Open Disk Utility. You can find it in Applications > Utilities or by searching with Spotlight.
- Choose View > Show All Devices.
- Examine the sidebar.
You may see several levels:
- Physical device: The actual external drive.
- Volume: The usable storage area on the drive.
- Disk image: A file that behaves like a disk, usually relevant to network backups.
If the physical drive appears
If the physical device appears but its volume is gray, select the volume and click Mount in the toolbar. Then check Finder and Time Machine again.
If Mount fails, select the volume and click First Aid, then click Run. First Aid checks the volume’s file-system structure and attempts repairs.
You can also run First Aid on the physical device if the volume check does not resolve the issue. Select the device in the sidebar, click First Aid, and follow the prompts.
Warning: First Aid is intended to repair file-system problems, but it cannot recover every failing drive. If the disk contains important backups and is making unusual noises, disconnecting, or repeatedly disappearing, avoid repeated repair attempts. Consider creating a copy of the disk or consulting a data-recovery professional.
If only the physical device appears
A missing volume can indicate damaged partition information or a disk that was erased or reformatted. Do not click Erase or Partition if the drive may contain backups you need. Those actions can destroy the existing backup data.
If the drive does not appear at all
If the physical device is absent from Disk Utility:
- Try another USB, USB-C, or Thunderbolt port.
- Try another known-good data cable.
- Connect the drive directly to the Mac instead of through a hub or dock.
- Test a different power adapter if the drive uses one.
- Test the drive on another Mac, if available.
If another Mac also fails to detect it, the enclosure, cable, power supply, or drive may be defective. If the drive appears on another Mac, the issue may involve your Mac’s port, adapter, hub, or macOS configuration.
Select the Backup Disk in Time Machine
A disk can be visible in Finder without being selected as Time Machine’s backup destination.
- Choose Apple menu > System Settings.
- Select General in the sidebar.
- Click Time Machine.
- Click Add Backup Disk or the Add Backup Disk button.
- Select the available disk.
- Follow the onscreen instructions.
The exact button shown can vary depending on whether a backup disk is already configured. If the disk is listed, select it and check its Time Machine settings.
If macOS asks whether to use the disk for backups, confirm only when you have selected the correct drive. If the disk contains existing backups, do not approve an option that says it will erase or replace the disk unless you intend to start over.
After selecting the disk, leave the Mac connected to power when practical and allow Time Machine time to prepare the backup. A large initial backup can take a while, especially over a network or with a slower hard drive.
For a new backup setup, see How to Back Up a Mac with Time Machine.
Verify the Disk’s Format and Available Space
Time Machine needs a writable destination with a file system macOS can use for backups. A disk formatted for another purpose may appear in Finder but not be offered by Time Machine, or it may require erasing before it can be used.
In Disk Utility, select the backup volume and review its details. The Format field identifies the file system. If the drive is nearly full, Time Machine normally removes older backups as space is needed, but a disk with file-system errors or insufficient usable space may still fail.
Warning: Formatting or erasing a disk deletes its contents. Do not erase the drive if it contains the only copy of existing backups or other files. Copy anything important elsewhere first.
If the disk is new and empty, or you have confirmed that its contents are no longer needed, you can use Disk Utility to erase and format it for Mac backups. The correct choice depends on the macOS version and the way you plan to use the drive. When in doubt, do not erase it until you have confirmed the needed format and have a separate copy of important data.
Troubleshoot a Network Time Machine Disk
Time Machine can use a shared disk or a supported network backup destination. Network disks require more than a working USB connection: the Mac must be connected to the same network, the server must be available, and the shared backup location must be accessible.
Try these steps:
- Confirm that the Mac is connected to the correct Wi-Fi or Ethernet network.
- Make sure the network device or Mac sharing the disk is powered on.
- Open Finder and check Network in the sidebar.
- Connect to the server or shared folder if it is not already visible.
- Open System Settings > General > Time Machine and check the selected destination.
- Restart the Mac and the network storage device if the destination remains unavailable.
A network backup may not appear immediately after waking from sleep or changing networks. If other shared folders are also unavailable, the problem is probably network or server related rather than specific to Time Machine.
Check for Permissions and Security Prompts
If the backup disk appears but Time Machine cannot write to it, macOS may be reporting a permissions, ownership, or access problem.
In Finder, select the disk and choose File > Get Info. Review the Sharing & Permissions section. Do not change permissions randomly, especially on a disk containing existing Time Machine backups. Changing ownership or access settings can make an existing backup set harder to use.
If macOS displays a prompt requesting access to an external disk, read it carefully and approve it only when you recognize the disk and action. If Time Machine reports that the destination is not available, remove and re-add the disk in System Settings > General > Time Machine after confirming that the disk is mounted.
Look for a Failing or Incompatible Drive
A drive that disappears during backups, disconnects when moved, or makes repeated clicking sounds may be failing. Warning signs include:
- Disk Utility reports input/output errors.
- The drive mounts and unmounts repeatedly.
- First Aid cannot complete.
- Backups stop at different points each time.
- The drive becomes unusually hot or noisy.
- The disk works only with one cable or at a particular angle.
Stop using the drive for routine backups if it contains the only copy of important data. If it still mounts, copy essential files or backups to another reliable disk before attempting more repairs.
Some older drives, encrypted volumes, third-party enclosures, and network storage systems may also have compatibility limitations. Check the drive manufacturer’s documentation for firmware, power, or enclosure requirements.
If Time Machine Still Cannot Find the Disk
Work through this final sequence:
- Restart the Mac.
- Connect the disk directly without a hub or dock.
- Try a different cable and port.
- Confirm that the physical device and volume appear in Disk Utility.
- Mount the volume manually if it is listed but unavailable.
- Run First Aid only after protecting important data.
- Re-add the disk under System Settings > General > Time Machine.
- Test the disk on another Mac.
- Replace the disk if multiple computers cannot detect it or if it shows signs of failure.
If the disk is visible but the backup history is missing, do not erase it immediately. Existing backups may still be recoverable even when Time Machine is not displaying them normally. You can also review How to Restore Files from a Time Machine Backup before making changes.
Frequently Asked Questions
Why is my Time Machine disk connected but not showing up?
The disk may not be mounted, may be hidden in Finder, or may not be selected as the Time Machine destination. Check Finder, then open Disk Utility and choose View > Show All Devices.
Why does the drive appear in Disk Utility but not in Time Machine?
The volume may be unmounted, formatted in a way Time Machine cannot use, damaged, or already configured for another purpose. Try Mount, run First Aid, and review the disk’s format. Do not erase it if it contains needed backups.
Will reconnecting the Time Machine disk delete my backups?
No. Disconnecting and reconnecting a healthy disk does not normally delete its data. Always eject the disk first when possible, and never disconnect it during an active backup.
Should I erase a disk that Time Machine cannot find?
Usually not as a first step. Erasing deletes the existing contents, including backups. Use it only when the disk is empty or you have verified that every needed file and backup exists elsewhere.
Can a faulty cable prevent Time Machine from finding the disk?
Yes. A damaged or incompatible cable can prevent the Mac from detecting the drive or cause repeated disconnections. Try a different cable that supports data transfer, not just charging.
What if the disk is missing from Disk Utility?
Test another port, cable, power source, and Mac. If the drive remains absent, the problem is likely hardware-related rather than a Time Machine setting.
Final Thoughts
Start with the cable, power, port, Finder, and Disk Utility before changing or erasing anything. If macOS detects the disk, mount it, check it with First Aid, and select it again in System Settings > General > Time Machine. Protect existing backups first: erasing the disk should be a last resort, not a troubleshooting shortcut.