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  • 1.  Need to change CPU-masking vmx parameters on the fly

    Posted Apr 09, 2013 07:32 PM

    In a migration scenario I need to change the CPU masks without a chance to poweroff the VMs for that changes.
    Is there a way to do that without crashing it ?

    I dont have the exact parameters yet but I can give them later.
    For now all hints are welcome



  • 2.  RE: Need to change CPU-masking vmx parameters on the fly

    Posted Apr 10, 2013 07:35 AM

    Hi Uli,

    Im not sure how to change the mask on the fly, but you can certainly supress the CPU compatibility checks by adding in a vCenter advanced setting ... I have used this method to save my bacon in the past - I will send you the exact parameters when I get to my desk, ETA 30min.

    I have actually tested this by doing a live migration between clusters of different CPU family ... ie, live migration from Intel Host to AMD host and visa versa ... I wouldn't recommend this as normal operations, but there are times when this is really handy.

    What it will give you is the opportunity to migrate a VM between hosts until you can schedule the downtime and reset the CPUID masks appropriately.

    Cheers,

    Jon



  • 3.  RE: Need to change CPU-masking vmx parameters on the fly
    Best Answer

    Posted Apr 10, 2013 08:19 AM

    These are vCenter advanced settings (set the value to false);
    Administration --> vCenter Server Settings --> Advanced Settings

    Here is the sledgehammer approach;

    config.migrate.test.CpuCompatibleWithHost
    - With this parameter set, all CPU-related compatibility testing throughout the vCenter Server is disabled.  If you have ESX/ESXi hosts on different hardware, the CPU compatibility won't be tested, and this could have serious knock-on impacts to the VMs.

    But you may want to look at using one of the following instead;

    config.migrate.test.CpuCompatibleMonitorSupport
    - With this parameter set, then "product version does not support features" errors will be suppressed, but other CPU compatibility errors will still be tested for.

    config.migrate.test.CpuCompatibleError
    - With this parameter set, then CPU compatibility warnings will still be displayed in the migrate wizard, but they won't block the migration.

    Cheers,

    Jon



  • 4.  RE: Need to change CPU-masking vmx parameters on the fly

    Posted Apr 14, 2013 10:15 AM

    Jon, this is awesome, many many thanks! ... I was looking for this kind of information for a very long time. All the instructions that are around for disabling vMotion compatibility checks do not work for vCenter 5.x, but these advanced settings really do the trick.

    I tested this in the lab, was really able to vMotion from AMD to Intel (and vice versa). And I had to write a blog post about this: http://www.v-front.de/2013/04/how-to-vmotion-from-intel-to-amd-and.html.

    - Andreas



  • 5.  RE: Need to change CPU-masking vmx parameters on the fly

    Posted Apr 15, 2013 09:34 AM

    Hi Andreas,

    Glad you found this useful :smileyhappy:

    Thanks for the blog post, this covers the topic comprehensively and has saved me posting a lengthy article on my own blog!

    Cheers,

    Jon



  • 6.  RE: Need to change CPU-masking vmx parameters on the fly

    Posted Apr 10, 2013 09:31 AM

    Hi Uli,

    you may try to do the change online via a PowerCLI script (see http://www.v-front.de/p/howtos.html#EditVMAdvCfg for an example) and then stun/un-stun the machine.

    As far as I known a stun/un-stun can not only be performed by a vMotion task, but also by creating/deleting a snapshot of the VM.

    - Andreas



  • 7.  RE: Need to change CPU-masking vmx parameters on the fly

    Posted Mar 03, 2014 11:54 PM

    Thank you for the info, but with the advanced settings in place I still receive the CPU compatibility errors that prevents the migration.  Do I need to enable EVC in both the source and target clusters for the settings to take effect?

    ~Eric