I just found a Cisco KB descripts a firmware issue may impact to ESXi FC storage performance. Please have a look whether your Cisco UCS system firmware is 2.1(2a), 2.1(2c), or 2.1(2d).
Balanced Memory Configuration for ESXi Servers
Background ESXi servers are fundamental infrastructure. The underly hardware performance has a butterfly effect on the upper layer virtual machines and applications. Since there is less than 10% performance overhead on the virtualization layer. So it’s valuable to get full performance on the hardware layer. Memory is a big player in hardware performance tuning. Balanced … Read more