At this time you need a computer. Its possible that later on some NAS units might have a package that can be installed.
But I would not go out and buy a NAS to do this. You can get very cheap SBC or desktop that you load linux on and connect the drives to them. You could for instance run a vault on each drive and not need to join them together like a NAS would. Some of these very small computers also have very low power consumption.