Understanding %busy / gstat

Hello,

System:

FreeNAS-9.2.1.6-RELEASE-x64 (ddd1e39)
Intel(R) Xeon(R) CPU E5-2603 v2 @ 1.80GHz
32GB RAM
X9DRi-LN4+/X9DR3-LN4+
AOC-SAS2LP-H8IR Controller + BBU
16 x WD20EFRX WD RED 2TB 3.5" SATA3 64MB CACHE

I'm having a serious problem with the speed of my storage. There is quite a bit happening read/write to the unit but I am confused as to how this relates to fixing things.

Please know this is a temporary setup and I am just using FreeNAS (in this instance) while the correct hardware is...

Understanding %busy / gstat