And what procedure was that?
The correct procedure is to use Packages->Alt-F in the webUI, specify one of the offered filesystems available and submit.
The Alt-F folder will be created at the root of the specified filesystem.
You can use any linux filesystem (ext2/3/4) on any disk, but the recommended procedure if to use a dedicated, always plugged USB flash stick
with a linux filesystem. The Disk->Wizard can prepare the USB stick for you, by selecting from the several disks *only* the USB stick and submitting.