Server virtualization/consolidation is becoming a norm and data centers and enterprises are now looking towards the horizon at how to bring dynamic, agile, and flexible capabilities to their IT infrastructure.
What I will focus on here is one specific technology that helps meet this goal called Live Migration, the capability to move active Virtual Machines (VMs) across a pool of physical servers with no downtime. If a VM is running on a server that is reaching high utilization or where resources are becoming constrained, Live Migration can migrate the active VM to a different physical server with absolutely no downtime. Now this is what I call truly dynamic and agile!
Unfortunately, in the past live migrations could only be accomplished between compatible systems (meaning systems with identical CPU microarchitecture). This is expected as you can’t move an application from one underlying architecture to another since new features are constantly incorporated into new CPUs and instructions sets are likely to have been updated/changed. Of course, you are likely to encounter compatibility issues which will interfere with live migration.
Intel VT FlexMigration (for Intel CPUs) and AMD‐V Extended Migration (for AMD CPUs) help resolve this issue. They ensure that the underlying hypervisor can expose a consistent set of instructions across all servers in the pool/cluster. Obviously, this is more convenient and efficient as now you can simply add new servers to the existing pool/cluster without having to worry about differences in CPU architecture.
Using VMware as an example, live migration is accomplished via VMotion technology. Starting with VMware Infrastructure 3 (ESX 3.5 Update 2 and VirtualCenter 2.5), VMware introduced Enhanced VMotion Compatibility (EVC). Taking advantage of Intel Flex Migration and AMD‐V Extended Migration technologies, EVC facilitates VMotion between different CPU generations. EVC will ensure that all CPUs within the pool/cluster are VMotion compatible.
Intel CPUs starting with Intel 45nm Core 2 (Penryn) incorporate Intel VT FlexMigration, and AMD CPUs starting with AMD Second Generation Opteron (revision E or F) incorporate AMD‐V Extended Migration.
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