I have not tested vmotion rigourously, but I would like to know under what circumstances does migration fail.
I can think of a scenario in which the available memory on the destination esx host is less than the sum of memory overhead caused by the VM and memory overhead caused by vmotion.
Under what other conditions does a migration fail ?
There are some items to look at when VMotion failed:
1. Make sure no devices currently mounted.
2. If VMotion with snapshot, you will receive error warnings but you will be able to VMotion just fine but might having hard time revert it back or commit.
3. Different types of CPU model (which can be done by using Enhance VMotion Compatability) or hide the CPU NX flags.
4. You didn't enable VMotion option on the port group.
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VMware vExpert 2009
iGeek Systems Inc.
VMware, Citrix, Microsoft Consultant
Likewise you need some excess CPU capacity on the destinatioin host, good network communication between the vmotion ports just to to add couple. The beautiful thing about vmotion is it checks for many things prior to starting and will fail if these conditions are there - and if failure occurs during the vmotion event before the vm moves it will stay on the originating esx server-
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