Mounting your USB/HDD as ext4 in your Zgemma will make your device unreadable when you next try and insert them in your computer. You can quickly fix this and most other corrupt USBs by correcting the USB partition.
In windows, open up command prompt with Administrator privileges
1. Go in Start > write “cmd” > right-click the Windows Command Prompt and choose to run it as an Administrator.
2. At the prompt, enter “DISKPART” to launch Microsoft’s disk management utility. It will take a second until it loads and when ready it will read “DISKPART>”.
3. Type in “list disk” to show a list of all disk drives. If your USB key is plugged into your PC, it should be listed here, along with other drives. Note the USB key’s disk number – you can pick it out by looking at the disk capacity.
4. Type “select disk n" (whatever is your USB disk number in place of "n").
5. Type “clean” for the utility to clean the disk, which DiskPart will confirm.
6. Create a new partition by entering “create partition primary”.
7. Choose this partition with “select partition 1", and then mark it as active by typing “active”.
8. Format the key by inputting “format fs=fat32". This should take a few minutes, and DiskPart will display a progress percentage.
9. Lastly, type “assign” to give this USB key a drive letter and “exit” to exit DiskPart.
If the above seems a bit technical google and download HDD guru low level format software and run that.
OR
Go into Disk management GUI on your PC, drop and create volume from there
Right click my
computer
Manage
Storage devices.
Pick the drive
Delete volume
New simple volume
Format
If right click on "My Computer" is not your thing then
Control panel
System
Admin tools
Computer Management