This article describes how to limit bandwidth for HCX Migrations.
HCX
VMC
In order to set a migration bandwidth limit you must enable the Wan-Opt appliance. Once that is enabled, the below "Advanced Configuration" section will become available.
I
The bandwidth change won’t take effect until the WO Appliance is redeployed. Redeploying the Wan-Opt flushes the cache and removes any benefit already learned. Keep this in mind when modifying this setting..