Workload Balancing (WLB) which was reintroduced in 6.5 is now enhanced with XenServer 7.x
Workload Balancing 7.2 is supported on XenServer 7.5 and includes the following enhanced features:
- Host disk Read/Write I/O. Introduces host disk Read/Write I/O recommendations for workload optimization to complement the existing CPU, memory, and network load balancing capabilities
- CentOS 7.2. Workload Balancing VPX is based on 64-bit CentOS 7.2

Details here: http://bit.ly/2sK6siq