Question about bottle neck in storage

[John Fleming]

Is there anyway to see how busy a SAS/Sata controller is vs disks? I
have a R720 with 14 Samsung 860 EVOs in it (its a lab server) in raid
10 ZFS.

When firing off a dd I (bs=1G count=10) seems like the disks never go
above %50 busy. I'm trying to figure out if i'm maxing out SATA 3 BW
or if its something else (like terrible dd options).

my setup is Dell R720 with 2 x LSI 9361 cards. Each card is going to a
dedicated 8 drive board inside the front of the R720. Basically i'm
just saying its not a single SAS cable to 14 drives.

Don't have cpu info hand.. zeon something. DDR3-1600 (128GB)

Both controllers are in 8x slots running PCIe gen 3.

BTW i'm sure this has been asked a million times but what would be
some decent benchmark tests while i'm at it?