Hi All 
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In the eleventh part of our series, we'll go through general concepts of Clustering in vSphere, as well as vMotion and Enhanced vMotion.
Credits:
- Frank Denneman
Now, Let's Start...
1. vMotion Configuration:
vMotion option must be enabled on the management port on every ESXi server involved in the process. Each VMKernel Port Group on each ESXi server involved in vMotion must have the same name to function correctly.
2. Enhanced vMotion:
Since vSphere 5.1, a new additional feature is available: Enhanced vMotion (XvMotion). It makes migrating VMs on local storages of ESXi hosts available even if these VMs are online and operational.
The following amazing article by Frank Denneman describing and deep diving in it:
http://frankdenneman.nl/2012/09/07/vsphere-5-1-vmotion-deepdive/
3. Enhanced vMotion vs. Storage vMotion:
This point may be not clear for the most of you, as was for me. A Storage vMotion will never move the compute state of a VM to another host while migrating the data disks from datastore to another. When you choose vMotion/Enhanced vMotion, that’s mean that you want to move a VM to another host, i.e. its compute state. It’ll either move the compute state only or move both the compute state and disks.
For a complete technical details, refer to Frank Denneman’s Article.
4. vMotion Multipathing:
When a VM is vMotion’ed, it can use multiple physical NICs by assigning many physical NICs to VMKernel ports used for vMotion on each host. Even if one vMotion occurs only at a time, all of pNICs are used for load distribution.
The following KB article by VMware is an easy step-by-step guide:
5. Enhanced vMotion Compatibility (EVC):
This feature is one of the most important features that must be enabled on any vSphere cluster. It controls the Physical CPU features that appear to each VM so that all VMs can be migrated easily between hosts (These hosts have different generations of CPUs) without need to power them down.
The following KB articles by VMware explain it sufficiently:
Keep in mind that, upgrading EVC generation to higher one is available, however, degrading it to lower one must be done when all VMs inside the cluster are powered off.
6. Removing CPU Constrains in vMotion by Overriding CPU Masks:
Using EVC, vSphere 5.0 and later allows vMotion of VMs on compatible-CPUs hosts. Sometimes and due to extreme corner cases, vMotion of VMs is required between two hosts with incompatible CPUs. This done by certain advanced operation called: Overriding CPU Masks. Each VM carries in its configuration certain mask defines characteristics of underlying physical CPU according to physical CPU generation called CPU Mask. By editing that mask, this VM can be migrated to another host with physical CPU with different characteristics and different generation. For more details, check KB article from VMware explaining it clearly:
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1993
Keep in mind that, vMotion can’t be done between hosts with physical CPUs from different vendors, i.e. Intel and AMD.
7. Troubleshooting vMotion Common Issues:
The following KB article from VMware summarizing all common issues of vMotion and their solutions in a single article:
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