Re: RAID level for SATA 1TB on CX4-120
Seeing that the enclosures are daisy chained together, before an LCC has a bottleneck issue, you'll probably see the entire bus have a bottleneck issue. The issue that you may or may not see would be with bandwidth. If your bus is running at 2Gbs/sec, then we are talking near 180-190MBs/sec before you exceed the bus. For a 4Gb, somewhere up near 380 MBs/sec. I am not sure of the exact numbers, just ballparking it.
I personally have been reviewing nars for performance cases for 3+ years and less than a handful of times have I found out the backend bus was the bottleneck. This is before EFD (SSD) drives came around though. With those and the right load you can quickly push a bus to the max if you are not careful.
For your setup, seeing you have just a single backend bus, you don't have the choice of crossing buses with the drives to spread out the load. Will you see and issue? Maybe or maybe not, it really depends.
Hope this helps.