How to set VirtualBox in order to access external hard drives in guest Win7?

I have installed VirtualBox in order to use Windows 7 as guest on a Macbook Air running Mavericks (mainly to be able to use a printer that has no drivers for Mac). Also, I have installed the Oracle_VM_VirtualBox_Extension_Pack and the Guest Additions, so that now the video settings as well as the support for USB are available. Except that, while the flash drives as well as the printer work, the external HDD drives connected by USB do not.

After un-mounting the external HDDs in Finder they appear only greyed out in VirtualBox system tray.

Adding them as filters in the Settings of the Virtual Machine makes them look selected as they should (no longer greyed out), but they are still not available in the guest Windows.

I am talking about two external HDD drives, both 500 GB, one ntfs and one fat32.

I expected the USB connections to work fully after installing the Extension_Pack and the Guest Additions, but it looks like there's something more to be done.

What?

Once I ejected the hard drive from mac os, it was instantly recognized by the guest windows virtual machine.

insert Guest Additions CD image.iso corresponding to your version number http://download.virtualbox.org/virtualbox/ worked for me once I unmounted USB from host OS launched VB, went into settings adding the USB filter and pointed to desired USB, launched VB, logged in to windows, voila, right there in computer devices as Drive (E:)

Host: MacBook Pro Summer 2014 with Mac OS Sierra 10.12.6 (has USB 3.0 ports). Guest: Windows 7 Professional 64-bit (I have not installed USB 3 capability yet).

Win7 would not recognise a USB 2.0 Kingston 16GB memory stick. I have VirtualBox extensions installed, and have added a USB device filter under VM settings. I have solved the problem by plugging a USB 2.0 hub into the MacBook Pro's USB 3.0 port, and then plugging the USB 2.0 memory stick into the hub. It works. (I have a Kensington PocketHub Mini USB 2.0 with 4 ports). Likewise I can now use a SanDisk Ultra USB 3.0 memory stick through the USB 2.0 hub.

This also solved a similar problem with an HP-Prime graphical calculator; the HP software on my mac would not see the calculator if it was plugged directly into the USB 3.0 port, but it was fine when I used the USB 2.0 hub.