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Server Virtualisation Support

IMan runs on a virtual server in the same way as on a physical one. Hyper-V and VMware each have a setting that hides the host's newer processor features from a virtual machine. IMan's services run on .NET, and .NET uses those features whenever the processor reports them. Check the setting on the virtual machine that runs IMan.

Hyper-V

Hyper-V's processor compatibility mode lets a running virtual machine move to a host with a different processor version. To make the move safe, the mode hides the processor instruction sets introduced in roughly the last ten years. For best performance, turn processor compatibility off on the virtual machine that runs IMan.

A new virtual machine starts with the mode off, and Microsoft recommends turning it on only for the duration of a migration. A hosting provider or cluster administrator may still have turned it on. Nothing inside the virtual machine can change the setting. If a hosting provider runs the host, ask them to check it.

Hyper-V accepts the change only while the virtual machine is off.

Hyper-V Manager

  1. Shut down the virtual machine.
  2. Select the virtual machine and click Settings.
  3. Under Hardware, expand Processor and select Compatibility.
  4. Untick Migrate to a physical computer with a different processor version.
  5. Click OK, then start the virtual machine.

System Center Virtual Machine Manager

  1. Shut down the virtual machine.
  2. Open the virtual machine's Properties and select Hardware Configuration.
  3. Select Processor. Under Compatibility, untick Allow migration to a virtual machine host with a different processor version.
  4. Click OK, then start the virtual machine.

PowerShell

Run these on the Hyper-V host, in PowerShell as an administrator:

Stop-VM -Name <VMName>
Set-VMProcessor -VMName <VMName> -CompatibilityForMigrationEnabled $false
Start-VM -Name <VMName>

To read the current setting:

Get-VMProcessor -VMName <VMName> | Select-Object CompatibilityForMigrationEnabled

Live migration across processor generations

With the mode off, the virtual machine moves to a host with a different processor version only while it is off. If it must live-migrate across a cluster with mixed processor generations, the mode has to stay on.

On a Windows Server 2025 cluster, use the dynamic mode for that case. The dynamic mode presents every processor feature that all the cluster's nodes share. The standard mode presents a fixed minimum set. The virtual machine needs configuration version 10.0 or later.

Set-VMProcessor -VMName <VMName> -CompatibilityForMigrationEnabled $true -CompatibilityForMigrationMode CommonClusterFeatureSet

VMware

Realisable has tested IMan on VMware and fully supports it there. If an issue turns out to be a VMware problem, the customer must take it to VMware support.

Enhanced vMotion Compatibility

VMware's equivalent of processor compatibility mode is Enhanced vMotion Compatibility (EVC). EVC sets a processor baseline for a vCenter cluster and hides every processor feature newer than the baseline. From vSphere 6.7, a virtual machine at hardware version 14 or later can also carry its own baseline. VMware calls this per-VM EVC.

VMware recommends leaving EVC on, because a cluster with EVC on can take hosts with newer processors later. EVC costs performance when its baseline is lower than the hosts need. A cluster that kept the baseline of hosts it has since retired hides features that every remaining host has. For best performance, set the mode to the highest that every host in the cluster supports, or turn EVC off.

To check the cluster's mode in the vSphere Client:

  1. Select the cluster and click the Configure tab.
  2. Under Configuration, select VMware EVC. The page shows the current mode.
  3. Click Edit to raise the mode or turn EVC off.

A virtual machine with its own baseline carries the same setting on its own Configure tab, under Settings and VMware EVC. Power the virtual machine off before you edit it.

In PowerCLI, these list the mode each cluster uses and the highest mode each host supports:

Get-Cluster | Select-Object Name, EVCMode
Get-VMHost | Select-Object Name, ProcessorType, MaxEVCMode

A running virtual machine keeps its old baseline until you power it off and on again. Restarting Windows inside it keeps the old baseline too.

Other Virtualisation Software Support

Other virtualisation products, such as Citrix XenServer, should work, but Realisable has not tested them. Most have a setting like the ones above. Check that the virtual machine sees the host's processor features.

For these products, Realisable supports issues known to occur on the native OS, and issues that the customer can show the virtualisation software does not cause. Support works as follows:

  • If an issue is a known IMan problem, Realisable Support will recommend the appropriate solution on the native OS.
  • If that solution does not work in the virtualised environment, Realisable Support will refer the customer to the virtualisation software's support.
  • If the issue is not a known IMan issue, Realisable Support will refer the customer to the virtualisation software's support.
  • When the customer can demonstrate the issue on the native OS, Realisable will resume support under its standard support terms.