read the explanation about what RAID 0 is, (aka not real RAID).
then think about the probability of a disk failing.
then think that you have four components in your drive array that must all work, the probability of any one failing at any time may have been 1 in 100, but since you have four drives, it's now 1 in 25. (you quadrupled your probability of catastrophic data loss) the loss of 1 disk means that the entire array is broken and you loose all your data.
Raid 0 does have it's place, where you need to create very large drives, for non-critical data.
with regards creating a massive, but potentially unstable four times more likely to break massive drive. and then splitting it up...
why did you need to create a massive drive and then split it up in to smaller drives?
the answer is probably, you never actually needed to create a 4TB drive in the first place?
why did I bet that you split that 4TB drive into smaller ones...? well it's pretty unlikely that you're running anything that needs a big block of data. at work we support some pretty big organisations, and it's rare that any of them require that sort of sized drive.
So I bet that because, you created the 4TB drive because you could, not because you needed it.
but then you did need a separate system and data drive, so you split your really big disk in two.