vMotion : Introduction

vMotion is the process of moving running virtual machines from one ESXi host to another.The disk files are not migrated(they stay in the shared storage), only the VMs memory and CPU processing moves from one server to another. In fact if you ping the VM while it is moving, you may at the most loose at most one or two ping packets.

vMotion happens in three stages:

-vCenter server verifies that teh VM is in a stable state
-VM state is copied over to the destinatiom. State includes the memory, registers and network connections
-VM is resumed in the destination host

vMotion can happen due to any of the following reasons:

- Balance the load on ESXi hosts using DRS
-When the VMs are being moved off from a host so that the host can be shutdown by DPM(distributed power management)
-You need to intsall patches using update manager or do a hardware maintenance, the VMs are migrated using vMotion and host is put into maintenance mose

vMotion requirements:

-You will need vSphere Essential plus,Standard, Enterprise or Enterprise plus license
-Shared storage between ESXi servers- iSCSI,FC or NFS.*
-VMkernal interface on both ESXi servers with vmotion enabled
- Same network label in source and destination hosts, either standard or distributed switches can be used
-CPU compatibility between hosts , or they need to be of the same processor family if you are planing to use Enhanced vMotion Compatibility(EVC). That means you cannot migrate VMs from a host with intel processor to a host with AMD processor.

*Starting with vSphere 5.1, vMotion without shared storage is possible, provided the destination host have access to the destination storage


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