vMotion Options in vSphere Web Client & vSphere Client

In vSphere Client:-

Option	Description
High Priority	On hosts running ESX/ESXi version 4.1 or later, vCenter Server attempts to reserve resources on both the source and destination hosts to be shared among all concurrent migrations with vMotion. vCenter Server grants a larger share of host CPU resources to high priority migrations than to standard priority migrations. Migrations always proceed regardless of the resources that have been reserved. On hosts running ESX/ESXi version 4.0 or earlier, vCenter Server attempts to reserve a fixed amount of resources on both the source and destination hosts for each individual migration. High priority migrations do not proceed if resources are unavailable.
Standard Priority	On hosts running ESX/ESXi version 4.1 or later, vCenter Server reserves resources on both the source and destination hosts to be shared among all concurrent migration with vMotion. vCenter Server grants a smaller share of host CPU resources to standard priority migrations than to high priority migrations. Migrations always proceed regardless of the resources that have been reserved. On hosts running ESX/ESXi version 4.0 or earlier, vCenter Server attempts to reserve a fixed amount resources on the source and destination hosts for each migration. Standard priority migrations always proceed. However, the migration might proceed more slowly or fail to complete if sufficient resources are not available.

In vSphere Web Client:-

Option	Description
Reserve CPU for optimal VMotion performance	vCenter Server attempts to reserve resources on both the source and destination hosts to be shared among all concurrent migrations with vMotion. vCenter Server grants a larger share of host CPU resources. if sufficient CPU resources are not immediately available, vMotion is not initiated.
Perform with available CPU resources	vCenter Server reserves resources on both the source and destination hosts to be shared among all concurrent migration with vMotion. vCenter Server grants a smaller share of host CPU resources. If there is a lack of CPU resources, the duration of vMotion can be extended.