Server for HA + NAS using Linux+Virtualbox

At my parent`s place I have a 32 bit Ubuntu Server with 2*2TB Raid-1 running since 2010. I have tested HA at my own server (64bit Ubuntu) using Virtualbox Headless Setup, working like a charm.
I would like to buy new hardware for my parents with the following requirements:

NAS with Samba Share and Raid-1 (possibly using SSDs nowadays), passive Cooling, Headless (ssh) operation, there is no screen attached to it in regular usage. Case can be ugly and big, since the device is in the basement any how. It should also last many years, so I would rather buy some CPU headroom.

Do you have ideas? My setup is a midi tower with passive Intel x64 CPUs, but I was wondering if one should use something ARM based?