Workload Balancing (WLB) which was reintroduced in 6.5 is now enhanced with XenServer 7.0.
Workload Balancing 7.0 is supported on XenServer 7.0, 6.5, 6.1, and 6.0 and it 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/2dqHD3y