In VMotion’s first iteration both the source and destination hosts need access to the same shared-storage. This limited the scope of VMotion to protocols like FC, iSCSI and NFS. It also meant possible limits around moving the VM from one vSphere Cluster to another vSphere Cluster – as in many cases the storage of one cluster isn’t visable to another. Many customers worked around this problem by having at least one datastore accessible to both clusters – often referred to in popular parlance as the “Swing LUN”. Later releases of vSphere have introduced the capacity to move VMs from host to another when there isn’t a common shared datastore – its wants sometimes referred to as a “shared nothing” environment.
Essentially, the Change Host and Datastore option chains together two processes – the SVMotion of the VMs file to another hosts, followed by the switching from one host to anther of the ownership of the running VM through the process of VMotion. This means it is possible to move a running VM on local storage on one host to different hosts local storage. Additionally, it also allows for the ability to move VMs from one cluster to another where no common shared storage exists.
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