recommended setup:
-
SSD1
Windows/Security : SSD Samsung PRO 512 GB if you can afford, 256GB would be fine
windows/Security update all the time, you need resilience and free space
SSD2
Game Install : SSD Samsung EVO 512GB + (depend on your needs)
this is only for modern demanding games like GC3, Witcher 3 and the like
HDD1
DATA : HDD Western Diggital Caviar Black, SMART mode (do not use RAID)
move My Documents/Downloads/Pictures/Videos/Music there for all users accounts
this is also where your save games go
HDD2:
GAME INSTALL : HDD Western Digital Caviar Black : as large as you can afford
this is where you should install your games the first time arround
only install to SSD if they load too slow. or if specified.
for example King of Fighter XIII need to be on SSD
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RECOMENDATIONS:
Caviar Black are the most reliable HD on the markets. They never break.
(In my lifetime 20+ years the 3 crash I witnessed were all Seagate)
SMART is best for gaming, it detect and fix problems.
RAID is a server technology to ensure constant data access over the internet.
It does not repair easily even for a pro.
what it does is redundancy. it need multiple HDs.
if one crash, it's gone 
SSD VERSUS HDD
It's complimentary.
SSD strength is mostly to load Windows + Security fast.
It increase response time versus threats.
Game wise SSD don't make a massive difference.
Unless load time is long due to large data size (HD install requirements)
for GC3 and Witcher3, a SSD is really useful.
