As I understand it, moving to NTA 4.0 and up and *should* place the flow storage database on separate hardware. I found Orion's suggested hardware requirements and got a Dell R430 build that I think fits the job. I'm looking for feedback.
PERC H730 RAID Controller, 1GB NV Cache
2x E5-2620 v3 2.4GHz,15M Cache,8.00GT/s QPI,Turbo,HT,6C/12T
64GB RAM 2133MT/s RDIMMs
8x 300GB 10K RPM SAS (2x in RAID1 for system, 6x in RAID10 for database)
If this is just for the NetFlow database, then it looks a little over the top, depending on how many collectors you'll have sending it updates and how many devices you'll be analysing the flows for of course.
That said, as with everything in IT, if you can afford it (read: get it past the bean counters) then more is always better