Samba shares and USB drives

I am very close to migrating the data on my bulky PC to my new Mac Mini fileserver and mounting the IDE drives in the USB drive brackets. Once I've done this, I will have the screenshots and data to write a nice "how to" on using the Mac Mini as a file server. There is however one slight problem which could prove to be a showstopper...

Samba test 1: local directories. I created a directory in the root of the HD in the mac mini, and made it R/W for everybody. Then, I used SharePoints to make it available to all password-less Guest users on the network (which happens to be the default Windows user for connecting to drives without asking for a password). All was well. I could access the share, and could copy as many files from as many machines imultaniously as I wanted.

Samba test 2: USB mounted volumes. I mounted a HFS+ formatted USB disk to the Mac Mini, and made it available to the network in the same way as in test 1. Everything seemed to be working fine and as expected, but while running some tests I discovered a strange thing: I can only copy files onto the USB drive from 1 machine at a time, 1 file at a time. When starting a new copy while allready in the process of copying an older file, one or both copy jobs crashed with a "file in use" error.

I am now trying to find out what is causing this problem. I have a firewire drive I can use to determine if it is the USB protocol or driver which is causing this problem, or if it is the fact that it is a mounted volume alltogether. If anybody has tips I'm glad to hear them. Meanwhile I'll be searching the web...

Update Using a firewire drive does not solve the problem. I did find some articles on fast user switching which state that only 1 user can access pheripherals at a time. This seems to be related to this problem.

Update 2 Creating a symlink to the mounted volume and sharing the link through samba will not change behaviour. I was expecting this, but tried anyway because it only costs 1 minute to test. Maybe a virtual drive would be an option. I can create virtual RAID disks in OSX, but I don't want my setup to be complex. This will add to the complexity when recovering from a sever crash. Simple, full and fast recovery from hardware problems is my top priority.