I run a linux distro firewall box that also acts as a file server and run into similar performance problems.

I suspect that your very neat little box has a native (ex2/ex3) file system and runs SAMBA on top to provide a windoze network file system.

SAMBA is not the fastest piece of software as it has to translate windoze commands to linux commands and map/emulate things like windoze file atributes under linux.

It may be that the box also supports nfs or some other network file system. Not sure if there is a windoze nfs package out there - but may be worth looking into.

One thing worth trying ... I have found that my anti-virus software imposes a significant overhead when copying/moving small files. I have found it very beneficial to turn off access scanning while moving files (assuming those files have been scanned and cleared sometime in the past).

Rgds,
Bob