filesystemmacbook prousb
I can't write to my USB on MacBook Pro. The USB was working well on both Windows and Mac until it stopped working on Mac suddenly (it's working well on Windows though). I reformatted it as FAT32 and tried other formats too (ExFAT,…etc) but, still facing the same issue.
Under "sharing and permissions", I find "you can only read" and it is greyed out so, I can't change it.
Any ideas are welcomed as I've been stuck in this since more than 2 weeks.
Plug the USB drive into any Windows computer.
Navigate to "My Computer" in Windows Explorer (click Start->My Computer[near the top right of the window]).
Right-click on the USB drive:
Click "Format".
Choose options you want to format as, make sure the "Read Only" button is deselected, and make sure the "Hidden" button is also deselected, and click "OK".
Congratulations! Your USB drive has now been re-formatted. You (should) now be able to format it using Mac OSX.
Simply use Disk Utility to format it as FAT, as Macs can indeed read and write to FAT drives–they just have problems with NTFS drives.
Insert your flash drive. Open Disk Utility (/Applications/Utilities/Disk Utility), select your flash drive in the sidebar, then click "Erase" in the top bar. Select "MS-DOS (FAT)" for your format, and Master Boot Record for your scheme.
Note that the FAT file system has a limitation of 4GB file size. If you want to circumvent this whilst still being able to use OS X, format the drive as exFAT (which has a file size limitation of 128 PiB). This option has been recently hidden with 10.11, so it takes a bit more work.
Open Terminal (/Applications/Utilities/Terminal). Run the command defaults write com.apple.DiskUtility advanced-image-options 1. This gives you access to hidden features within Disk Utility. Open Disk Utility (/Applications/Utilities/Disk Utility), select your flash drive in the sidebar, then click "Erase" in the top bar. Select "ExFAT" for your format, and Master Boot Record for your scheme.
Best Answer
I have seen that issue (disk being read-only on Mac and read-write on Windows) before where it was caused by a slight disk corruption.
I solved it by plugging the USB drive into a Windows PC and running scandisk to check for and correct errors on the drive. Afterwards the drive worked just fine on both Mac and Windows for reading and writing.
Note that it is important to "safely eject" the drive whenever you want to disconnect the drive from the Mac or PC. On the Mac, you'll need to press the small up-arrow besides the drive name in Finder (called unmounting). On the PC you'll need to look in the dock for the icon for safe ejecting hardware, select your drive and eject it. Another option is to power down the PC/Mac whenever you want to unplug the drive, but that is cumbersome.
If you do not safely eject the drive, you risk corrupting the drive.