Intel FlexMigration - Redux (aka not working on any ESX version)

[i4004]

We have three servers using Penryn class processors (Xeon 5450's / 3Ghz

/ 12mb L3 *support for FlexMigration*) and STILL cannot migrate/

vmotion live hosts from a Dual Core Xeon 5160 which is also within the

Core 2 Duo family. Our Xeon 5450/Penryn servers are Dell 2950's series

III running ESX 3.5u1/patched and our Xeon 5160 based servers are Dell

2950's series I running ESX 3.0.2 also [patched to the hilt.

The idea was to replace our Dell 2950 Series I DC/16GB RAM servers

with Dell 2950 Series III QC/32GB RAM servers and vmotion machines off

the slightly older Dell onto the ESX farm and back again. All

possible with FlexMigration, right? WRONG!!!

The issue deals with SSE4.1 and the fact that VMware ESX 3.5u1 is

supposed to fully support it - experimental support was included in ESX

3.0.1 via a binary module (as seen here:

http://forums.amd.com/forum/messageview.cfm?catid=203&threadid=92023

*password required for reference*).

What exactly is going on here? Do we need to enable something to

get the so-called FlexMigration CPU compatibility method that VMotion

under VC 2.5 supposedly supports? We know all to well VMware's KB

article 1993 (

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1993

) but changing CPU masks at the VM level requires the machine to be off

and once a machine is off/powered down we can migrate it ANYWAY to

another server in our farm without issue.

Any idea what's going on here?

Thanks,

Gerson Ricardo

[Matthias_Hausne]

Ricardo,

While 3.5u1 makes use of Intel FlexMigration, the UI is still the same as in previous releases. In order to migrate the VM, you'll have to manually define a CPU feature mask that masks the SSE4.1 CPU feature. The KB article says that this is not recommended, however, 3.5u1 can reliably hide the feature so you (and your VM) should be fine. There is no way around powering off the VM. (From the viewpoint of the VM, you are removing the SSE4.1 feature. The only way to do this is to power off the guest and power it on again on the new virtual CPU that has fewer features.)

Hope this sheds some light on the issue,

Matthias

[i4004]

Give your statement that "While 3.5u1 makes use of Intel FlexMigration, the UI is still the same as in previous releases.." in what exact way does FlexMigration get used currently in ESX 3.5u1 as its only apparent purpose is to allow Vmotion across CPU's with dissimilar processor stepping, which isn't working now at all?

Please do note that your statement is in direct conflict with the return answer that the VMware tech support dept sent me earlier this week, posted above - do you perhaps have a updated news on the matter?

Also, when you state that "UI is the same as in previous releases.." are you talking about the VC 2.5 UI or some other aspect of the VI3 foundation? If so is there some manual Vmotion method to make use of Vmotion with FlexMigration from, say, the console? Please do tell!

Cordially,

Gerson Ricardo

Gables Engineering, Inc.

[Matthias_Hausne]

The VMware tech support answer is the one that counts.

What I'm trying to say is that from the Virtual Center UI perspective, nothing has changed between VI 3.5 (and possibly even VI 3) with respect to specifying CPUID masks for VMs. Under the hood, VI 3.5u1 is using FlexMigration to hide CPU feature bits from guest software, whereas earlier releases did not use FlexMigration. The net effect is that hiding the SSE4.1 bit from a guest can be done reliably in 3.5u1, whereas it could not be done reliably in earlier releases of VI.

Please note though that even with FlexMigration, you can never mask additional CPUID feature bits while the VM is running. You will always have to power off the VM, hide the bit, and then power on again. Once the VM is powered on and the SSE4.1 bit is masked, you can VMotion between machines with and without SSE4.1 support. In releases prior to VI3.5, this was not recommended or supported; in 3.5u1 you should be able to safely VMotion between these machines.

Hope this helps/clarifies.

[JonRoderick]

You might be interested to know that VC 2.5 U2 has some enhanced Vmotion capabilities (EVC) that make more use of the flexmigration technology (though I can't get it to work - LOL).