There are a few common reasons why you may be unable to transfer files from your Mac to an external hard drive:
The external drive is not properly formatted
For full compatibility with Mac OS, an external hard drive needs to be formatted in a file system Mac can read and write to. The most common file systems for external hard drives used with Mac are:
– APFS (Apple File System): The default file system for flash drives and SSDs formatted on modern versions of Mac OS. Provides full read/write compatibility with Mac.
– exFAT: A widely compatible file system that works well for external hard drives used with both Windows and Mac. However, does not support permissions and other Mac-specific features.
– FAT32: An older Windows-compatible file system supported by Mac. However, has a 4GB per-file size limit making it unsuitable for larger files and Time Machine backups.
– NTFS (Windows NT File System): The default Windows file system that Mac can read but cannot write to without third-party software. Not recommended for external hard drives to be used with Mac.
If your external drive is formatted with an incompatible file system like NTFS, you will be able to read files on the drive but not write to it from your Mac. You will need to reformat the drive in a compatible file system.
How to check external drive format on Mac
To check what file system your external drive is currently formatted with:
1. Connect the external drive to your Mac if not already connected
2. Launch Finder and go to Applications > Utilities and open Disk Utility
3. Select the external drive on the left sidebar in Disk Utility
4. Check the ‘Format’ listed for the drive, such as ‘APFS’, ‘FAT32’, etc. This is the current format of the drive
If the format is incompatible, you will need to reformat the drive before you can fully read/write files on your Mac.
How to format an external drive for Mac
To format your external hard drive for use with Mac:
1. Connect the drive to your Mac and launch Disk Utility
2. Select the drive on the left sidebar and click ‘Erase’ along the top toolbar
3. For ‘Format’ select ‘APFS’ or ‘exFAT’ depending on your needs
4. Give the drive a name and click ‘Erase’
5. The drive will be formatted and ready for use with your Mac
Reformatting the drive will erase all existing data, so make sure to backup any important files first. APFS is optimized for Mac while exFAT has broader compatibility with Windows and Mac.
The external drive has errors
If your external drive has logical errors, file system corruption, bad sectors, or physical damage, this can prevent your Mac from being able to fully read/write files to it.
Some signs of errors on your external drive:
– You get error messages when trying to access files
– Files appear as corrupted or missing
– Drive is read-only or unmountable
– Strange noises coming from the drive
– Frequent beachballing/freezing when using drive
How to check external drive for errors on Mac
To check an external drive for errors on Mac:
1. Open Disk Utility
2. Select the external drive and click ‘First Aid’
3. Click ‘Run’ – this checks and repairs file system errors
If First Aid is unable to fix the errors, your drive likely has physical damage or worsening failures. At that point, you should backup your data and replace the damaged drive.
You can also try reformatting the drive after backing up your data. But if errors reappear, then there is likely irreversible hardware damage.
Drive is corrupted after unsafe ejection
On Mac, you should always properly eject and disconnect external drives before unplugging them. If you disconnect the drive without ejecting, it can lead to file system corruption and data errors.
Some signs of corruption after unsafe ejection:
– Mounting errors when reconnecting drive
– Missing/inaccessible files
– ‘Disk Not Ejected Properly’ error messages
If this occurs, reconnect the drive to Mac and try the following:
How to repair corrupted drive on Mac
1. Open Disk Utility
2. Select the corrupted external drive
3. Click ‘First Aid’ > ‘Run’ to check and repair errors
4. If errors persist, reboot computer and run First Aid again
5. Try reformatting external drive if still facing corruption issues
Always remember to properly eject the drive before disconnecting to avoid further corruption.
Incompatible USB ports/cables
If you are connecting your external drive using an incompatible USB cable, port, or hub this can prevent your Mac from mounting, reading, and writing to the drive properly.
Some things to check:
– Try connecting the drive to rear USB-A ports directly if using older Mac models. The rear ports are version 3.0+ compatible on newer Macs.
– Avoid low power USB ports like those on keyboards or frontside Mac ports. These may not provide enough power for larger external drives.
– Inspect USB cable – a damaged/faulty cable can cause connectivity issues. Try connecting with a different high-quality USB 3.0 cable.
– Avoid using USB hubs and connect drive directly to Mac ports. Hubs can sometimes interfere with external drive connections.
– For latest Macs with USB-C/Thunderbolt 3, use recommended adapters if drive requires USB-A connectivity.
Using supported ports and cables will provide full compatibility and speed when transferring files between a Mac and external drive.
Drive requires external power supply
Larger high capacity external hard drives often require a separate power connection to function properly, besides just the data USB cable.
If your drive did not come with an external power supply/adapter, make sure to check the drive documentation to confirm if one is needed.
Trying to power a drive solely through the USB data cable can result in:
– Drive not mounting or dropping out during usage
– File transfer issues and errors
– Corrupted data or drive damage over time
– Not enough power to spin up larger hard drive mechanisms
Using a Y-cable USB with two connectors can sometimes provide enough extra power for drives without a separate power input. But better to follow recommended power requirements for your specific external hard drive model.
Mac computer going to sleep during transfer
If your Mac goes to sleep/standby mode during a file transfer, this can interrupt the data transfer and result in file errors or corruption.
To prevent this:
– Disable sleep/standby mode before starting lengthly file transfers
– Change sleep settings to never put hard drives to sleep
– Use a third party app like Amphetamine to keep system awake
– Manually wake computer if it starts going to sleep during transfer
Allowing the computer to sleep during file transfers between Mac and external drives can lead to interrupted transfers, OS errors, and data corruption.
Problem with connected USB hub/dock
Using a USB hub or docking station to connect your external drive can sometimes cause connectivity issues with Mac.
Some things to check if connecting drive through a USB hub:
– Try connecting drive directly to Mac instead of through hub
– Ensure hub is powered – preferably with external power adapter
– Check that hub/dock is compatible with your Mac model and OS version
– USB hubs can cause power delivery issues to connected drives
– Disconnect other devices from hub during drive transfer
– Troubleshoot/replace damaged or faulty hub if issues persist
For reliable external drive connectivity, your Mac’s own USB ports are recommended over third-party hubs and docks whenever possible.
Damaged external drive USB connector
Over time, frequently plugging/unplugging an external drive can damage the USB connector. A loose, damaged, or faulty USB port on the external drive enclosure can prevent proper connection and data transfer.
If USB port damage is suspected:
– Inspect USB plug pins for any bent/broken/corroded pins
– Check USB port on enclosure for any loose/damaged contacts
– Try connecting with another USB cable if available
– Test USB drive on another computer to rule out other issues
– Contact drive manufacturer about possible RMA/replacement if issue persists
Avoid forcing plug when connecting drive or undue strain on USB port. If damage occurs, drive enclosure may need replacement to restore full connectivity.
Drive requires data recovery services
If your external drive has severe logical corruption or physical damage, this may require professional data recovery in order to retrieve your data or get the drive functioning again.
Some signs that advanced data recovery could be required:
– Mechanical failure sounds from drive (clicking, beeping, grinding)
– Drive not powering on at all
– Severe corruption causing most files to be unreadable
– Failed drive components like read/write heads, motor, PCB
– Physical damage like fire/water exposure, smashed platters
In these cases, do not attempt DIY repair. Specialized data recovery firms have the tools and cleanroom facilities to safely extract data from damaged drives and determine if repairs are possible.
However, data recovery can be expensive and is not guaranteed. Always backup important data to avoid reliance on drive recovery services.
Anti-virus software interfering
Some anti-virus and security programs can end up blocking access to external drives connected to your Mac. This leads to issues like:
– Drive not showing up or mounting in Finder
– Read/write permissions errors
– Files not copying properly
Check your security software settings and see if any drives are incorrectly being identified as suspicious or malicious devices. Whitelist your external drive by adding it to the allowed devices list in your anti-virus program preferences.
Also add exceptions for your drive to any active firewalls or ransomware protection features that could be blocking access. Turning off overzealous security features temporarily can help determine if they are the cause of connectivity problems.
OS version incompatibility
Using an external drive formatted with a newer file system than your Mac supports can lead to transfer issues and limited usage.
For example, an APFS formatted drive will not work with OSX versions before High Sierra. And NTFS drives require extra software for write access on Mac.
Check your Mac OS version and confirm the drive format is supported. If necessary, reformat the external drive to a compatible file system your Mac can fully read and write to.
Updating to the latest Mac OS release can allow usage of modern file systems on external drives. But reformatting may still be required for full cross-platform usage.
User account lacks permissions
The user account you are logged into on your Mac may not have full read/write permissions to access content on the external drive.
This could happen if:
– Drive is formatted with NTFS and permission controls are active
– Another user on your Mac formatted the drive
– Permissions were accidentally restricted
– Parental controls are blocking external drives
Check the permission settings on the files/drive you are trying to access. If needed, add your user account to have proper access.
Also authenticate as an Admin user or disable parental controls/privacy restrictions that could be blocking the drive. Log out and back in after making account changes.
Time Machine backup in progress
If your external drive is currently being used as a backup destination for Time Machine, transfers will be blocked while a backup is actively in progress.
Wait for the Time Machine backup session to finish before trying to access or move files on that drive.
You can also exclude the drive from backups to allow transfers while keeping it available as a backup destination when not actively connected.
Pausing/disabling Time Machine schedules can also prevent drive access conflicts while you need to transfer data. Just remember to turn automatic backups back on when done.
Drive formatted for Windows
External hard drives formatted specifically for Windows (NTFS) will have only limited read-only support on Mac by default.
Trying to copy files from Mac to a Windows NTFS drive will fail unless you install extra software to enable Mac write support.
To fully transfer data between Windows drives and Mac, format the drive using a compatible cross-platform file system like exFAT instead. This allows full read/write on both OS.
If you need to retain NTFS for Windows use, enable NTFS write support on Mac using paid solutions like Paragon NTFS or Tuxera NTFS.
Auto-mount settings not enabled
For external drives to appear in Finder on connection, the Mac auto-mount settings need to be enabled:
1. Go to System Preferences > General
2. Check ‘External disks’ under ‘Show these items on desktop’
3. Also check the ‘Connect hard disks’ and ‘Connect optical drives’ options
If these are not enabled, external drives will fail to mount automatically when connecting via USB.
Double check auto-mount settings if your drive is not appearing as normal on connection.
Duplicate drive names
If you have multiple external drives with the exact same name, Mac can have issues identifying and mounting the correct drive.
When connecting multiples drives, make sure each drive has a unique name assigned to avoid conflicts.
If you have duplicate names, rename one or both of the drives to something distinct. Avoid generic names like “External” that provide no uniqueness.
Uniquely named drives are especially important for users that routinely connect many different external drives to a Mac.
Thunderbolt/USB-C problems
Mac models with USB-C/Thunderbolt 3 ports require compatible cables, adapters and hubs to properly connect external USB drives.
Some troubleshooting tips for Thunderbolt/USB-C connections:
– Use recommended USB-C to USB-A adapters from Apple or other manufacturers
– Ensure Thunderbolt cable, dock or hub supports USB data transfer speeds
– Check that USB-C ports are Thunderbolt 3 compatible if drive requires Thunderbolt connectivity
– Try different USB-C ports in case one is damaged or has faulty power delivery
– Reinstall USB/Thunderbolt controller drivers if issues persist in connecting USB drives
Getting the right adapters and cables is crucial for connectivity with USB-C/Thunderbolt 3 Macs when using traditional USB-A drives.
Faulty USB ports/controllers
Like any hardware component, the USB ports on your Mac are subject to occasional failures which can affect external drive connections.
Some signs of USB port/controller faults:
– USB devices randomly disconnecting/reconnecting
– Unable to access drives on one or more USB ports
– Drive not detected errors on specific ports
– USB device connection issues after a Mac OS update
– Physical damage to USB port preventing access
If you can isolate the issue to one specific problematic USB port, avoid using that port for drives and get it repaired if under warranty.
Reinstalling USB controller drivers, SMC/NVRAM resets, and Mac OS reinstalls can also help resolve stubborn hardware-level USB faults impacting drives.
Drive requires reformatting
As a last resort, completely reformatting the external drive may be required to resolve persistent connectivity or file transfer issues from Mac.
Note: Reformatting will erase all data on the drive. Backup important files first.
Steps to reformat external drive on Mac:
1. Backup data from external drive if possible
2. Open Disk Utility
3. Select external drive and click Erase
4. Choose APFS or exFAT format
5. Rename drive if desired and click Erase
6. Drive will be wiped and reformatted for Mac
Reformatting can fix file system errors, corrupted data, partition issues that may be impacting drive connectivity. But backup important data first as this will erase the drive.
Conclusion
There are a number of reasons why you may be unable to transfer files from a Mac to an external hard drive. The most common issues involve incompatible file system formats, drive errors/corruption, physical connectivity problems with cables or USB ports, power supply issues, and software conflicts.
To resolve file transfer problems, first check your drive format, cables used, USB connections, auto-mount settings, and any security software that could block access. Also inspect the external drive for errors using Mac’s Disk Utility and run First Aid to check and repair issues if found.
Reformatting the external drive is recommended if you continue experiencing data transfer failures or connectivity issues from your Mac. Just be sure to backup your data first before erasing the drive. Following best practices for drive connections, avoiding forceful drive ejections, and maintaining updated Mac OS versions can also help maximize external drive reliability for hassle-free file transfers and backups.
