Possibly the biggest, badest retro disk server is Drivewire 4, (originally to serve disks for the Tandy Color Computer.) It's written in Java and serves far more than just disk. It can take about anything that's a serial data stream and serve it to its client. MIDI, telnet, printer... And of course, disk.
This one took a little fiddling to make it work on CHIP. The full SWT GUI in Drivewire 4 seems to have issues on CHIP, so the config.xml has to be edited by hand to specify DeviceType as "serial" and SerialDevice as "/dev/ttyUSB0"
(Basically use the Raspberry PI instructions for CHIP :)
Drivewire fortunately also has a lightweight GUI built-in so once the serial port specifics are good the liteui is sufficient.
As far as the SWT issues go, I think it needs a file called swt-pi.jar to complete the SWT to GTK interface. I've found instructions on building this jar (step 1: install eclipse. Nope.) but nowhere it can just be downloaded.