If you have an older PC or Laptop that you're not using you can load FreeNAS on it and get a bit of experience.

http://www.freenas.org/

I had a Lenovo with a couple of external USB drives attached running as a NAS for a while and it worked well.

NetApp also has a simulator you can download to get some experience with their frontend. This is all more towards the storage side rather than DBA side but it's pretty easy to learn the basics.