Generally speaking, if the disk is formatted with Mac-friendly file system and the setups are correct, you will be able to both read and write to the external disk. However, when you attach an external drive like an external hard drive or a pen drive to Mac, only to find that the Mac won’t let you write to it. We will tell you how to troubleshoot the read-only problem for external drives in three ways. Keep reading.
Check if the disk is NTFS-formatted
NTFS works well on Windows platform, but it is a different story on Mac machines. The NTFS write support is disabled by default, so you can only read the NTFS-formatted disks on Mac. You cannot modify, delete, or rename the existing files nor create new files on the disk.
To check if it is the NTFS file system that prevents you from writing to the disk, Right-click the disk on the desktop and select “Get Info”. You will find the disk’s format in the information window.
To solve the incompatibility between NTFS file system and Mac OS, you can use Disk Utility to reformat the disk to exFAT or FAT, both of which are fully compatible with Windows and Mac. After reformatting, the disk should be readable and writable on Mac. However, if you have many important files on the NTFS-formatted disk and it takes you long time to back up them, the easier way is to use a third-party NTFS for Mac driver like iBoysoft NTFS for Mac.
Unlike open-source drivers, iBoysoft NTFS for Mac doesn’t require any installation of other programs nor running command lines. It is super simple to download and install because it is a light-weight menu bar utility. After launching it, you can have full read and write access to NTFS disks without any limitations. Additionally, the utility allows you to open, mount, unmount, repair and format the NTFS drives. With it, you can also reformat other disks to NTFS on Mac if you have a such need. The utility works on macOS 10.15/10.14/10.13/10.12 and earlier OS X versions to 10.8.
Ignore the read-only permission
After logging in the Mac operating system, each user can set up permissions to disks. If somebody has set up a read-only permission to the disk without telling you, you probably will end up with read-only access to a disk, to which you are supposed to have full read and write access. In this case, if you want to write to the external disk, you need to ignore the read-only permission that was set up.
To change the permission for the external disk, right-click the external disk and select “Get Info”. Scroll down to the “Sharing & Permissions” section to see if you only have read-only privilege on this disk. If so, click on the lock icon to authenticate. Then check the box saying “Ignore ownership on this volume.” Then click on the “Read only” beside your account to select “Read & Write”.
Fix the disk errors
When the solutions above cannot solve the read-only situation for your external drive, it might result from disk errors. Minor disk errors may prevent the Mac from mounting the disk in read and write mode to protect your data. To solve the problem, the first thing you should do is to back up your files as soon as possible, because it is very possible that the disk is going to be corrupted.
Then you can run First Aid in Disk Utility to fix the disk errors. If the First Aid fails, you can also use Erase option to reformat the disk to completely eliminate the errors.
The methods introduced here should help you out of the read-only situation for external drives on Mac.