Your Mac will create an invisible Trash folder on any removable storage you attach to it. This includes USB sticks, digital cameras, USB hard disks, non-Apple cellphones, and so on — basically, anything that appears under the DEVICES heading in Finder.
The result is that, if you delete files using Finder when the storage is attached, they won’t actually be deleted. Instead they’ll merely be moved to this invisible Trash folder. Do this enough times and the storage device gets filled-up, even though it might appear as if there’s only a few (or no!) files on it. Confusion reigns!
Here’s a trick to stop OS X trashing things on the removable storage. This means any files you drag to the Trash from the removable storage device will be eradicated immediately.
Note that these steps assume the storage device is formatted with FAT32/64, which is usual for removable storage devices. The steps also permanently delete the Trash on the device (although not the main Trash on your hard disk), so ensure there’s nothing there that you’re hoping to salvage.
Here are the steps:
1. Attach the removable storage device. It will appear under the DEVICES heading on the left of the Finder window. Make a note of its name.
2. In the Finder window, hit Shift+Command+G, then type /Volumes/. You’ll see listed all the storage devices attached to your system.
3. Open a Terminal window. You’ll find this in the Utilities folder within the Applications list of Finder.
4. In the Terminal window, type cd, then a space. Hold down Command, then click and drag from the Finder window the entry in the main listing relating to the storage device. Position the mouse cursor over the Terminal window and release the mouse button.
5. In the terminal window type the following exactly as it’s written!
rm -rf .Trashes/ && touch .Trashes
And that’s all that’s needed. Remember that these steps must be repeated once for each storage device you insert. When you drag files from the storage device to the Trash, you’ll now see a message warning that they’ll be permanently deleted.
Should you want to restore Trash to the removable storage device, repeat Steps 1-4 above, then type the following:
Files you delete will now be Trashed in the way you’d expect.