Home > Storage > PowerMax and VMAX > Storage Admin > Dell PowerMax and VMware vSphere Configuration Guide > VMware Storage Distributed Resource Scheduler
Take note when Host I/O Limits are set on storage groups that contain devices that are part of a datastore cluster that uses SDRS. When SDRS is used, all devices that are in that datastore cluster should have the same Host I/O Limit. Moreover, the devices should come from the same PowerMax. This recommendation is given because the Host I/O Limit throttles I/O to those devices. This configuration may be done to limit applications on those devices from impacting other devices on the array or perhaps to simplify QoS management. A datastore cluster may contain devices from the same or a different array that do not have a Host I/O limit. During its balancing that SDRS may relocate virtual machines on those limited devices to nonlimited devices. Such a change might alter the wanted QoS or permit the applications on the virtual machines to exceed the wanted throughput. It is prudent to have device homogeneity when using Host I/O Limits together with SDRS.