Speed up VirtualBox Shared Folders on XP Guests

I’m using a Windows XP guest in VirtualBox in a intensive way for a few days. The host and guest exchange their files via a shared folder. It’s a very convenient way to exchange data between virtual machines and the guest. In my case, the shared folders reside on an encrypted file system: guests do not have to care of security.

An alternative to shared folders is to use file servers like NFS or SMB (Samba). But they require a network interface configured as ‘host networking’, need maintenance and extra configuration. A limitation to shared folders is the file protection: files stored in shared folders are simply owned by the UID running the virtual machine. A shared folder access can be defined as read-write or read-only, nothing else. To support multiple users, SMB or NFS must be implemented. But it wasn’t a requirement in my case.

Under Windows XP, my shared folder is simply mapped to a drive letter using the following command:

C:\> net use s: \\vboxsvr\shared_folder /persistent:yes

I faced a very annoying problem: When trying to access the drive, it took from time to time ~30 seconds to display the files! Same issue when saving files from applications (the dialog boxes timed out too often).

I posted my problem to the VirtualBox forum and got a solution (it’s more a quick fix):

In your Windows XP guest, edit the ‘hosts’ file (located in c:\windows\system32\drivers\etc) and replace the line:

127.0.0.1   localhost

with this one (where my_hostname is your host computer name):

127.0.0.1   localhost vboxsvr my_hostname

Now, the time to access the share has been reduced to two or three seconds, which is more acceptable.

But I would like to understand how work the shared folders. I sniffed traffic on loopback interface at the host level and did not see any relevant traffic. Does anybody has more information?