well, i do try and keep all my data hot in the server.. i am using the devices as redundancy, so no raid anywhere. 24Tb with 3 copies.
ive got a couple of 6-bay readynas i got second hand and a plain ol' ubunutu workstation i crammed with 6 drives and an ssd.
app server runs off 6 local disks(and an ssd for os) which are replicated to the 2 nas as logical (they pull), the workstation gets a drive-for-drive physical