On Monday I gave you a pointer to a great resource on configuring network QoS in converged networking configurations. One thing that this documentation does not cover is how to configure QoS for Live Migration over SMB.
If you are using Live Migration over SMB, and storing virtual machine hard drives on SMB shares, then both of these traffic flows will be covered by the SMB QoS policy. However, they should not be treated the same. Live Migration is designed to use all the network bandwidth it can – and some of that bandwidth needs to be reserved for virtual machine storage traffic. Fortunately, Windows Server 2012 R2 includes tools that allow you to do just this.
Jose Barreto discusses this in detail on his blog post here: http://blogs.technet.com/b/josebda/archive/2014/08/11/smb3-powershell-changes-in-windows-server-2012-r2-smb-bandwidth-limits.aspx
The SMB Bandwidth Limits feature can be installed with either Server Manager or PowerShell. Once installed – you can use the “Set-SMBBandwidthLimit” parameter to restrict the maximum throughput of Live Migration.
But what is the right limit to set? That is hard to say, and varies from deployment to deployment. On one hand – if you set the limit too low, you will slow down Live Migration in your environment. If you set it too high – you will see storage performance impacts while Live Migrating virtual machines. Personally, I would recommend setting this to between 60 and 80% of the available network bandwidth.