Not all space available on USB storage devices after deleting partitions

[miretogo]

I have two external USB storage devices:

* 16 GB USB stick (flash drive)
* Old 2.5 inch 80 GB HDD

I performed the following procedure with Disk Utility on both devices:

* Delete existing partition.
* Create a maximum-size new partition.

Afterwards, Disk Utility's "Partition" tab shows for both devices that about 5 GB are not available:

* 16 GB USB stick: 10.06 of 15.47 GB available (-> 5.41 GB missing)
* Old 2.5 inch 80 GB HDD: 74.1 of 79.68 GB available (-> 5.58 GB missing)

Since about 5 GB are unavailable on both devices and since 5 GB is about the size of the last few Mac OS installers (Yosemite, Mavericks, etc.), I wonder if having used these devices in the past to install Mac OS has created something like hidden partitions that cannot be easily removed.

What do you think?

 

[Weaselboy]

Try selecting the drive itself (like where it says Sandisk in my screenshot), and not just the partition. Then in the erase tab erase the entire disk. That should wipe anything on there.

 

[miretogo]

Thanks for your suggestion, Weaselboy. However, it doesn't seem to have any effect. For example, after erasing the USB stick, Disk Utility still states in the "Partition" tab that there is one partition named "Untitled", with a size of 15.47 GB, of which 10.06 GB are available.



PS: In the screenshot, "," is used as decimal mark instead of "." because I live in Germany.

 

[Weaselboy]

Thanks for your suggestion, Weaselboy. However, it doesn't seem to have any effect. For example, after erasing the USB stick, Disk Utility still states in the "Partition" tab that there is one partition named "Untitled", with a size of 15.47 GB, of which 10.06 GB are available.

View attachment 512975

PS: In the screenshot, "," is used as decimal mark instead of "." because I live in Germany.

That blue shaded area in mine is out of whack also (showing about 1/3 in use on an empty drive) but when you select Untitled it shows the correct amounts for me. What do you see when you select the Untitled volume?

Try running this command in Terminal and it will show what folders are there and how much space each uses.

sudo du -d 1 -x -c -g /Volumes/Untitled/

I get this on a fresh erase.

1	/Volumes/Untitled//.fseventsd
1	/Volumes/Untitled//.Spotlight-V100
0	/Volumes/Untitled//.Trashes
1	/Volumes/Untitled/
1	total

 

[miretogo]

Thanks again for your reply, Weaselboy. Using your command, I get exactly the same output as you do.

I think this phenomenon is too obvious to be a Disk Utility bug, so there must be another explanation.

Using the instructions in this article (http://osxdaily.com/2011/09/23/view-mount-hidden-partitions-in-mac-os-x/), I discovered that there is also a partition called "EFI" (extensible firmware interface) on the USB stick. However, it has only a capacity of 209.7 MB.