NAS Help

Hello, people on the TekSyndicate Forums.

My friend needs a NAS for his firm.
-It will be accessed by less than 8 people at any time locally, and needs to be accessible off-site.
-While massive amounts of storage space is not necessary (about 2TB will be fine), data integrity is very important, as it will be storing logs and client information.
-I would like it to be expandable.
-Physical size isn't really an issue, although smaller is preferable.

Given these things, what kind of configuration would you recommend (both hardware and software)? I was looking into pre-built solutions, but expandable ones seem to be quite expensive.

Thanks in advance.

This is a little dated in terms of hardware, but it's a good place to start in terms of what is commonly recommended.